103 results on '"Alan D. Wanamaker"'
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2. Importance of Weighting High-Resolution Proxy Data From Bivalve Shells to Avoid Bias Caused by Sample Spot Geometry and Variability in Seasonal Growth Rate
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Bernd R. Schöne, Soraya Marali, Regina Mertz-Kraus, Paul G. Butler, Alan D. Wanamaker, and Lukas Fröhlich
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bivalve sclerochronology ,shell ,element chemistry ,seasonal growth rate ,weighted average ,arithmetic average ,Science - Abstract
Shells of bivalve mollusks serve as archives for past climates and ecosystems, and human-environmental interactions as well as life history traits and physiology of the animals. Amongst other proxies, data can be recorded in the shells in the form of element chemical properties. As demonstrated here with measured chemical data (10 elements) from 12 Arctica islandica specimens complemented by numerical simulations, mistakes during sclerochronological data processing can introduce significant bias, adding a further source of error to paleoenvironmental or biological reconstructions. Specifically, signal extraction from noisy LA-ICP-MS (Laser Ablation—Inductively Coupled Plasma—Mass Spectrometry) data generated in line scan mode with circular LA spots requires a weighted rather than an arithmetic moving average. Otherwise, results can be in error by more than 41%. Furthermore, if variations of seasonal shell growth rate remain unconsidered, arithmetic annual averages of intra-annual data will be biased toward the fast-growing season of the year. Actual chemical data differed by between 3.7 and 33.7% from weighted averages. Numerical simulations not only corroborated these findings, but indicated that arithmetic annual means can overestimate or underestimate the actual environmental variable by nearly 40% relative to its seasonal range. The magnitude and direction of the error depends on the timing and rate of both seasonal shell growth and environmental change. With appropriate spatial sampling resolution, weighting can reduce this bias to almost zero. On average, the error reduction attains 80% at a sample depth of 10, 92% when 20 samples were analyzed and nearly 100% when 100 samples were taken from an annual increment. Under some exceptional, though unrealistic circumstances, arithmetic means can be superior to weighted means. To identify the presence of such cases, a numerical simulation is advised based on the shape, amplitude and phase relationships of both curves, i.e., seasonal shell growth and the environmental quantity. To assess the error of the offset induced by arithmetic averaging, Monte Carlo simulations should be employed and seasonal shell growth curves randomly generated based on observed variations.
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- 2022
- Full Text
- View/download PDF
3. Ragweed and sagebrush pollen can distinguish between vegetation types at broad spatial scales
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Hannah M. Carroll, Alan D. Wanamaker, Lynn G. Clark, and Brian J. Wilsey
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Ambrosia ,Artemisia ,ecoregions ,paleoecology ,pollen ratio ,prairie ,Ecology ,QH540-549.5 - Abstract
Abstract Patterns of vegetation distribution at regional to subcontinental scales can inform understanding of climate. Delineating ecoregion boundaries over geologic time is complicated by the difficulty of distinguishing between prairie types at broad spatial scales using the pollen record. Pollen ratios are sometimes employed to distinguish between vegetation types, although their applicability is often limited to a geographic range. The Neotoma Paleoecology Database offers an unparalleled opportunity to synthesize a large number of pollen datasets. Ambrosia (ragweed) is a genus of mesic‐adapted species sensitive to summer moisture. Artemisia (sagebrush, wormwood, mugwort) is a genus of dry‐mesic‐adapted species resilient to drought. The log pollen ratio between these two common taxa was calculated across the North American midcontinent from surface pollen samples housed in the Neotoma Paleoecology Database. The relative proportion of Ambrosia has roughly doubled since European settlement, likely due to widespread disturbance, while Artemisia proportions are nearly unchanged. Correcting surface samples for the disturbance signal in modern Ambrosia proportions will allow Ambrosia, a strong indicator of summer moisture, to be more accurately represented. In surface samples where both Ambrosia and Artemisia are reported as nonzero proportions of the pollen sum, mean annual precipitation explains approximately 78% of the variation in the log Ambrosia‐to‐Artemisia ratio. Application of this model to Little Ice Age pollen samples produces precipitation reconstructions which generally agree with reconstructions from independent non‐pollen proxies. In addition, we find that modern ecoregions within the North American midcontinent can be successfully distinguished from one another using the log Ambrosia‐to‐Artemisia ratio. These relationships can improve reconstructions of past climate and improve delineation of past ecoregion boundaries.
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- 2020
- Full Text
- View/download PDF
4. A MODERN MULTICENTENNIAL RECORD OF RADIOCARBON VARIABILITY FROM AN EXACTLY DATED BIVALVE CHRONOLOGY AT THE TREE NOB SITE (ALASKA COASTAL CURRENT)
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David C Edge, Alan D Wanamaker, Lydia M Staisch, David J Reynolds, Karine L Holmes, and Bryan A Black
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Archeology ,General Earth and Planetary Sciences - Abstract
Quantifying the marine radiocarbon reservoir effect, offsets (ΔR), and ΔR variability over time is critical to improving dating estimates of marine samples while also providing a proxy of water mass dynamics. In the northeastern Pacific, where no high-resolution time series of ΔR has yet been established, we sampled radiocarbon (14C) from exactly dated growth increments in a multicentennial chronology of the long-lived bivalve, Pacific geoduck (Paneopea generosa) at the Tree Nob site, coastal British Columbia, Canada. Samples were taken at approximately decadal time intervals from 1725 CE to 1920 CE and indicate average ΔR values of 256 ± 22 years (1σ) consistent with existing discrete estimates. Temporal variability in ΔR is small relative to analogous Atlantic records except for an unusually old-water event, 1802–1812. The correlation between ΔR and sea surface temperature (SST) reconstructed from geoduck increment width is weakly significant (r2 = .29, p = .03), indicating warm water is generally old, when the 1802–1812 interval is excluded. This interval contains the oldest (–2.1σ) anomaly, and that is coincident with the coldest (–2.7σ) anomalies of the temperature reconstruction. An additional 32 14C values spanning 1952–1980 were detrended using a northeastern Pacific bomb pulse curve. Significant positive correlations were identified between the detrended 14C data and annual El Niño Southern Oscillation (ENSO) and summer SST such that cooler conditions are associated with older water. Thus, 14C is generally relatively stable with weak, potentially inconsistent associations to climate variables, but capable of infrequent excursions as illustrated by the unusually cold, old-water 1802–1812 interval.
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- 2022
5. Twentieth-century Azores High expansion unprecedented in the past 1,200 years
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Nathaniel Cresswell-Clay, Caroline C. Ummenhofer, Diana L. Thatcher, Alan D. Wanamaker, Rhawn F. Denniston, Yemane Asmerom, and Victor J. Polyak
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General Earth and Planetary Sciences - Published
- 2022
6. Resistant calcification responses of Arctica islandica clams under ocean acidification conditions
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Yi-Wei Liu, Alan D. Wanamaker Jr., Sarah M. Aciego, Ian Searles, Thor Arne Hangstad, Melissa Chierici, and Michael L. Carroll
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Aquatic Science ,Ecology, Evolution, Behavior and Systematics - Published
- 2023
7. Atlantic circulation change still uncertain
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K. Halimeda Kilbourne, Alan D. Wanamaker, Paola Moffa-Sanchez, David J. Reynolds, Daniel E. Amrhein, Paul G. Butler, Geoffrey Gebbie, Marlos Goes, Malte F. Jansen, Christopher M. Little, Madelyn Mette, Eduardo Moreno-Chamarro, Pablo Ortega, Bette L. Otto-Bliesner, Thomas Rossby, James Scourse, Nina M. Whitney, Universitat Politècnica de Catalunya. Departament de Física, and Barcelona Supercomputing Center
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Informàtica::Aplicacions de la informàtica [Àrees temàtiques de la UPC] ,Canvis climàtics -- Atlàntic, Regió de l' ,Física [Àrees temàtiques de la UPC] ,Palaeoceanography ,Physical oceanography ,Climatic changes -- Atlantic Ocean Region ,General Earth and Planetary Sciences ,Palaeoclimate ,Climate-change impacts - Abstract
Deep oceanic overturning circulation in the Atlantic (Atlantic Meridional Overturning Circulation, AMOC) is projected to decrease in the future in response to anthropogenic warming. Caesar et al. 1 argue that an AMOC slowdown started in the 19 th century and intensified during the mid-20th century. Although the argument and selected evidence proposed have some merits, we find that their conclusions might be different if a more complete array of data available in the North Atlantic region had been considered. We argue that the strength of AMOC over recent centuries is still poorly constrained and the expected slowdown may not have started yet. K.H.K. acknowledges funding from NOAA grant NA20OAR4310481. D.E.A. and B.L.O.-B. acknowledge support from the National Center for Atmospheric Research, which is a major facility sponsored by the National Science Foundation under cooperative agreement no. 1852977. N.M.W. acknowledges support from a NOAA Climate and Global Change Postdoctoral Fellowship. M.F.J. acknowledges support from NSF award OCE-1846821 and C.M.L. acknowledges support from NSF award OCE-1805029. This is UMCES contribution 6062. Peer Reviewed Article signat per 17 autors/es: University of Maryland Center for Environmental Science, Chesapeake Biological Laboratory, Solomons, MD, USA: K. Halimeda Kilbourne / Department of Geological and Atmospheric Sciences, Iowa State University, Ames, IA, USA: Alan D. Wanamaker / Geography Department, Durham University, Durham, UK: Paola Moffa-Sanchez / Centre for Geography and Environmental Sciences, University of Exeter, Penryn, UK: David J. Reynolds, Paul G. Butler & James Scourse / Climate and Global Dynamics Laboratory, National Center for Atmospheric Research, Boulder, CO, USA: Daniel E. Amrhein & Bette L. Otto-Bliesner / Woods Hole Oceanographic Institution, Falmouth, MA, USA: Geoffrey Gebbie & Nina M. Whitney / Cooperative Institute for Marine and Atmospheric Studies, University of Miami, Miami, FL, USA: Marlos Goes / Atlantic Oceanographic and Meteorological Laboratory, National Oceanic and Atmospheric Administration, Miami, FL, USA: Marlos Goes / Department of the Geophysical Sciences, The University of Chicago, Chicago, IL, USA: Malte F. Jansen / Oceanography Department, Atmospheric and Environmental Research, Inc., Texas, TX, USA: Christopher M. Little / US Geological Survey, St Petersburg Coastal and Marine Science Center, St Petersburg, FL, USA: Madelyn Mette / Barcelona Supercomputing Center, Barcelona, Spain: Eduardo Moreno-Chamarro & Pablo Ortega / Graduate School of Oceanography, University of Rhode Island, Kingston, RI, USA: Thomas Rossby / University Corporation of Atmospheric Research, Boulder, CO, USA: Nina M. Whitney
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- 2022
8. Life histories and niche dynamics in late Quaternary proboscideans from midwestern North America
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Stacey Lengyel, Kayla Kolis, Alan D. Wanamaker, J. Douglas Walker, Jeffrey J. Saunders, Greg Hodgins, and Chris Widga
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Marine isotope stage ,Ecological niche ,Extinction ,Arts and Humanities (miscellaneous) ,Pleistocene ,Ecology ,Megafauna ,General Earth and Planetary Sciences ,Last Glacial Maximum ,Glacial period ,Quaternary ,Geology ,Earth-Surface Processes - Abstract
Stable isotopes of mammoths and mastodons have the potential to illuminate ecological changes in late Pleistocene landscapes and megafaunal populations as these species approached extinction. The ecological factors at play in this extinction remain unresolved, but isotopes of bone collagen (δ13C, δ15N) and tooth enamel (δ13C, δ18O, 87Sr/86Sr) from midwestern North America are leveraged to examine ecological and behavioral changes that occurred during the last interglacial-glacial cycle. Both species had significant C3 contributions to their diets and experienced increasing levels of niche overlap as they approached extinction. A subset of mastodons after the last glacial maximum exhibit low δ15N values that may represent expansion into a novel ecological niche, perhaps densely occupied by other herbivores. Stable isotopes from serial and microsampled enamel show increasing seasonality and decreasing temperatures as mammoths transitioned from Marine Isotope Stage (MIS) 5e to glacial conditions (MIS 4, MIS 3, MIS 2). Isotopic variability in enamel suggests mobility patterns and life histories have potentially large impacts on the interpretation of their stable isotope ecology. This study further refines the ecology of midwestern mammoths and mastodons demonstrating increasing seasonality and niche overlap as they responded to landscape changes in the final millennia before extinction.
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- 2020
9. Eutrophication Drives Extreme Seasonal CO2 Flux in Lake Ecosystems
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John A. Downing, Clayton J. Williams, Ana M. Morales-Williams, and Alan D. Wanamaker
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0106 biological sciences ,Total organic carbon ,chemistry.chemical_classification ,Biogeochemical cycle ,010504 meteorology & atmospheric sciences ,Ecology ,Lake ecosystem ,010603 evolutionary biology ,01 natural sciences ,Carbon cycle ,chemistry ,Environmental chemistry ,Dissolved organic carbon ,Environmental Chemistry ,Environmental science ,Ecosystem ,Organic matter ,Eutrophication ,Ecology, Evolution, Behavior and Systematics ,0105 earth and related environmental sciences - Abstract
Lakes process a disproportionately large fraction of carbon relative to their size and spatial extent, representing an important component of the global carbon cycle. Alterations of ecosystem function via eutrophication change the balance of greenhouse gas flux in these systems. Without eutrophication, lakes are net sources of CO2 to the atmosphere, but in eutrophic lakes this function may be amplified or reversed due to cycling of abundant autochthonous carbon. Using a combination of high-frequency and discrete sensor measurements, we calculated continuous CO2 flux during the ice-free season in 15 eutrophic lakes. We found net CO2 influx over our sampling period in 5 lakes (− 47 to − 1865 mmol m−2) and net efflux in 10 lakes (328 to 11,755 mmol m−2). Across sites, predictive models indicated that the highest efflux rates were driven by nitrogen enrichment, and influx was best predicted by chlorophyll a concentration. Regardless of whether CO2 flux was positive or negative, stable isotope analyses indicated that the dissolved inorganic carbon pool was not derived from heterotrophic degradation of terrestrial organic carbon, but from degradation of autochthonous organic carbon, mineral dissolution, and atmospheric uptake. Optical characterization of dissolved organic matter revealed an autochthonous organic matter pool. CO2 influx was correlated with autochthony, while efflux was correlated with total nitrogen and watershed wetland cover. Our findings suggest that CO2 uptake by primary producers during blooms can contribute to continuous CO2 influx for days to months. Conversely, eutrophic lakes in our study that were net sources of CO2 to the atmosphere showed among the highest rates reported in the literature. These findings suggest that anthropogenic eutrophication has substantially altered biogeochemical processing of carbon on Earth.
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- 2020
10. Trophic dynamics of a reservoir fishery following an introduction of a top predator: Insights from stable carbon and nitrogen isotopes
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Randall D. Schultz, Joseph E. Morris, Alan D. Wanamaker, James J. Wamboldt, and Hannah M. Carroll
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Ecology ,biology ,Niche ,chemistry.chemical_element ,Aquatic Science ,Hybrid striped bass ,biology.organism_classification ,Isotopes of nitrogen ,Fishery ,chemistry ,Littoral zone ,Environmental science ,Carbon ,Apex predator ,Trophic level - Published
- 2020
11. Hydroclimate variability from western Iberia (Portugal) during the Holocene: Insights from a composite stalagmite isotope record
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Victor J. Polyak, Diana L. Thatcher, Jonathan Haws, Alan D. Wanamaker, David P. Gillikin, Daniel Fullick, Yemane Asmerom, Rhawn F. Denniston, and Caroline C. Ummenhofer
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Archeology ,Global and Planetary Change ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Ecology ,Isotope ,Paleontology ,Stalagmite ,15. Life on land ,010502 geochemistry & geophysics ,01 natural sciences ,Arid ,13. Climate action ,Physical geography ,Holocene ,Geology ,0105 earth and related environmental sciences ,Earth-Surface Processes - Abstract
Iberia is predicted under future warming scenarios to be increasingly impacted by drought. While it is known that this region has experienced multiple intervals of enhanced aridity over the Holocene, additional hydroclimate-sensitive records from Iberia are necessary to place current and future drying into a broader perspective. Toward that end, we present a multi-proxy composite record from six well-dated and overlapping speleothems from Buraca Gloriosa (BG) cave, located in western Portugal. The coherence between the six stalagmites in this composite stalagmite record illustrates that climate (not in-cave processes) impacts speleothem isotopic values. This record provides the first high-resolution, precisely dated, terrestrial record of Holocene hydroclimate from west-central Iberia. The BG record reveals that aridity in western Portugal increased secularly from 9.0 ka BP to present, as evidenced by rising values of both carbon (δ13C) and oxygen (δ18O) stable isotope values. This trend tracks the decrease in Northern Hemisphere summer insolation and parallels Iberian margin sea surface temperatures (SST). The increased aridity over the Holocene is consistent with changes in Hadley Circulation and a southward migration of the Intertropical Convergence Zone (ITCZ). Centennial-scale shifts in hydroclimate are coincident with changes in total solar irradiance (TSI) after 4 ka BP. Several major drying events are evident, the most prominent of which was centered around 4.2 ka BP, a feature also noted in other Iberian climate records and coinciding with well-documented regional cultural shifts. Substantially, wetter conditions occurred from 0.8 ka BP to 0.15 ka BP, including much of the ‘Little Ice Age’. This was followed by increasing aridity toward present day. This composite stalagmite proxy record complements oceanic records from coastal Iberia, lacustrine records from inland Iberia, and speleothem records from both northern and southern Spain and depicts the spatial and temporal variability in hydroclimate in Iberia.
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- 2020
12. Using light stable isotopes to assess stream food web ecology in a general ecology laboratory course
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Hannah M. Carroll, Suzanne Ankerstjerne, Alan D. Wanamaker, and Derek D. Houston
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δ13C ,Natural materials ,Stable isotope ratio ,Ecology ,Ecology (disciplines) ,05 social sciences ,050301 education ,050109 social psychology ,δ15N ,Food web ,Education ,Energy flow ,0501 psychology and cognitive sciences ,General Agricultural and Biological Sciences ,0503 education - Abstract
Stable isotopes in natural materials provide a powerful way to study energy flow in many systems and are widely used in fields such as archaeology, ecology, forensics, geochemistry, geology, oceano...
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- 2019
13. Reprint of Unexpected isotopic variability in biogenic aragonite: A user issue or proxy problem?
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Alan D. Wanamaker, Jared Ballew, Nina M. Whitney, and Madelyn J. Mette
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education.field_of_study ,010504 meteorology & atmospheric sciences ,δ13C ,δ18O ,Aragonite ,Population ,Sampling (statistics) ,Geology ,Replicate ,engineering.material ,010502 geochemistry & geophysics ,Atmospheric sciences ,01 natural sciences ,Isotopes of oxygen ,13. Climate action ,Geochemistry and Petrology ,engineering ,14. Life underwater ,Transect ,education ,0105 earth and related environmental sciences - Abstract
The present study seeks to investigate sources of isotopic variability in the commonly used paleoclimate archive, the marine bivalve Arctica islandica, with an emphasis on the potential of human-induced variability arising from sampling techniques. Stable carbon (δ13Ccarbonate) and oxygen (δ18Ocarbonate) isotopes were analyzed for split (intra-sample) and replicate (intra- and inter-shell) samples taken from a group of laboratory-reared individuals, a natural population from northern Norway, and a natural population from the Gulf of Maine, USA. Compared to analytical uncertainty of 0.17‰ and 0.30‰ for δ13C and δ18O, respectively, among the natural populations, the mean difference between shell splits and shell replicates ranged from 0.12‰ and 0.33‰ for δ13C and δ18O, respectively. Our data suggest that heterogeneity of the carbonate material (i.e., large range of isotopic composition within one sample due to seasonal environmental variability) may contribute to “unexpected” variability more than human-induced error from sampling imprecision when collecting whole annual increments. Furthermore, δ13C from juvenile shells were highly variable (2σ standard deviation = 0.65‰), approximately four times more variable than analytical precision. High precision among δ18O measurements of the laboratory-reared shells confirm the presumption that shells reliably and consistently precipitate in isotopic equilibrium with ambient seawater. Monte Carlo simulations of measurements from this population allowed characterization of improvements in uncertainty at increasing levels of replication. Substantial reduction in uncertainty occurs when increasing from two to three shells, however replication using a total of four shells further decreased uncertainty to within the 99% confidence level. Published studies sometimes compensate for uncertainties by replicating records over multiple individuals or multiple transects within the one individual. Oftentimes, however, isotope records are constructed from single individuals or transects and therefore fail to provide thorough estimates of proxy error. Our findings suggest that replication of carbon and oxygen isotope measurements of contemporaneously produced aragonite is necessary in order to reduce proxy-derived noise. Furthermore, population-specific estimates of uncertainty related to natural variability among individuals should be investigated in order to provide more realistic representations of proxy noise when reporting isotope time series.
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- 2019
14. Strontium, magnesium, and barium incorporation in aragonitic shells of juvenile Arctica islandica: Insights from temperature controlled experiments
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Alan D. Wanamaker and David P. Gillikin
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Strontium ,010504 meteorology & atmospheric sciences ,biology ,Ocean current ,chemistry.chemical_element ,Geology ,Barium ,010502 geochemistry & geophysics ,biology.organism_classification ,01 natural sciences ,Isotopes of oxygen ,Salinity ,Isotopic signature ,chemistry ,13. Climate action ,Geochemistry and Petrology ,Environmental chemistry ,Seawater ,14. Life underwater ,Arctica islandica ,0105 earth and related environmental sciences - Abstract
In order to constrain spatial and temporal temperatures and environmental conditions in the North Atlantic Ocean during the Holocene, high-resolution (seasonal to annual) marine proxies with excellent chronological constraints are needed. The long-lived ocean quahog, Arctica islandica, which has the potential to provide a precise annually-dated record, via crossdating techniques, is a fairly well-developed and tested marine proxy archive. In particular, oxygen isotopes derived from A. islandica shell carbonate have provided a wealth of information on marine climate and ocean circulation dynamics, however, shell-derived oxygen isotopes are influenced by both the isotopic source water signature (covarying with salinity) and seawater temperature. If seawater isotopic signature is not known, temperature reconstructions become challenging. Thus, an independent technique to estimate past seawater temperatures is highly desired, however based on previous studies on adult and juvenile clams, the utility of elemental ratios in A. islandica shell material as environmental proxies remains questionable. To further evaluate the influence of seawater temperature on elemental and isotopic incorporation during biomineralization, A. islandica shells were grown at constant temperatures under two regimes during a 16-week period from March 27 to July 21, 2011 at the Darling Marine Center in Walpole, Maine. Individual juvenile clams were stained with calcein and cultured at 10.30 ± 0.30 °C for six weeks. After this, the clams were again stained with calcein and cultured at 15.00 ± 0.40 °C for an additional 9.5 weeks. Average salinity values were 30.20 ± 0.70 and 30.70 ± 0.70 in the first and second phases of the experiment, respectively. Continuous sampling within and across the temperature conditions (from 10.30 °C to 15.00 °C) coupled with the calcein markings provided the ability to place each sample into a precise temporal framework and to establish exact average growth rates for the shells sampled. After accounting for changes in the isotopic composition of seawater, oxygen isotopes from one sampled shell effectively recorded seawater temperatures during the study and also gave confidence to the temporal fit of the data. Elemental ratios (Sr/Ca, Mg/Ca, Ba/Ca) from five aragonitic shells were determined via laser ablation inductively coupled plasma mass spectrometry. Sr/Ca and Mg/Ca data showed little coherence with temperature during the culture experiment, including the rapid 5 °C increase in seawater temperature. However, Ba/Ca ratios showed an inverse relationship with seawater temperatures although this relationship was noisy. Additionally, salinity interactions were present during the 15.00 °C treatment, further highlighting complex incorporation of elements during biomineralization. Incorporation of Sr, Mg, and Ba were strongly and variably impacted by growth rates. Combined, the results from these culture experiments demonstrate that Sr/Ca, Mg/Ca, Ba/Ca ratios in juvenile A. islandica shell material are dominated by physiological processes and thus not reliable as environmental proxies.
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- 2019
15. Chemical sclerochronology
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David P. Gillikin, Alan D. Wanamaker, and C. Fred T. Andrus
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Geochemistry and Petrology ,Geology - Published
- 2019
16. A Multicentennial Proxy Record of Northeast Pacific Sea Surface Temperatures From the Annual Growth Increments of Panopea generosa
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Christine Outridge, David J. Reynolds, Richard Weng, Bryan A. Black, Daniel Griffin, Dominique Bureau, Alan D. Wanamaker, Bethany C. Stevick, and David C. Edge
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Atmospheric Science ,Panopea generosa ,010504 meteorology & atmospheric sciences ,0207 environmental engineering ,Paleontology ,02 engineering and technology ,Oceanography ,01 natural sciences ,Annual growth % ,Sclerochronology ,Environmental science ,020701 environmental engineering ,Proxy (statistics) ,0105 earth and related environmental sciences - Published
- 2021
17. Persistent Multidecadal Variability Since the 15th Century in the Southern Barents Sea Derived From Annually Resolved Shell‐Based Records
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Alan D. Wanamaker, William G. Ambrose, Michael L. Carroll, Carin Andersson, Michael J. Retelle, and Madelyn J. Mette
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biology ,Shell (structure) ,Oceanography ,biology.organism_classification ,Isotopes of oxygen ,Geophysics ,Space and Planetary Science ,Geochemistry and Petrology ,Sclerochronology ,Earth and Planetary Sciences (miscellaneous) ,Little ice age ,Arctica islandica ,Geology - Published
- 2021
18. Paired bulk organic and individual amino acid δ15N analyses of bivalve shell periostracum: A paleoceanographic proxy for water source variability and nitrogen cycling processes
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Alan D. Wanamaker, Nina M. Whitney, Beverly J. Johnson, Katherine Luzier, and Philip T. Dostie
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010504 meteorology & atmospheric sciences ,biology ,Periostracum ,δ15N ,010502 geochemistry & geophysics ,biology.organism_classification ,01 natural sciences ,Isotopes of nitrogen ,chemistry.chemical_compound ,Oceanography ,chemistry ,Geochemistry and Petrology ,Paleoclimatology ,Environmental science ,Carbonate ,Bivalve shell ,Nitrogen cycle ,Arctica islandica ,0105 earth and related environmental sciences - Abstract
Developing high-resolution, well-dated, marine proxies of environmental, climatic, and oceanographic conditions is critical in order to advance our understanding of the ocean’s role in the global climate system. While some work has investigated bulk and compound specific stable nitrogen isotope (δ15N) values in bivalve shells as proxies for environmental variability, the small concentrations of nitrogen found in the organic matrix of the shell calcium carbonate (hereafter carbonate) makes developing high resolution records challenging. This study investigates the potential of using the bulk and amino acid δ15N values of bivalve periostracum, the protein layer on the outside of the shell, as a proxy archive of nitrogen cycling processes and water source variability. Bulk δ15N values were measured on the periostracum, carbonate, and adductor muscle of Arctica islandica shells collected in the Gulf of Maine. Increased variability of isotopic values across growth lines compared to along growth lines support mechanistic reasoning based on growth processes that periostracum is recording changes in δ15N values over the course of the clam’s lifetime (up to 500 years). In addition, the statistically significant relationship between periostracum δ15N values and contemporaneous carbonate δ15N values of the same shell (r = 0.82, p Compound specific δ15N analyses of the periostracum of A. islandica shells were used to determine that the calculated trophic position of the clams in this study (1.4 ± 0.4) did not change significantly between 1783 and 1997. Phenylalanine δ15N values over the last 70 years show similar trends to that of the bulk record, suggesting that changes in bulk δ15N values over that time period are related to changes in baseline δ15N values. Periostracum δ15N values from shells collected in the western Gulf of Maine have decreased by ∼1‰ since the mid-1920s. This trend (−0.008‰/year) is not statistically different from the trend of previously published δ15N values of deep-sea corals from the entrance to the Gulf of Maine over the same time period. This coral record has been shown to indicate a shift in water source in the region and therefore the similarity between the two records suggest that changes in periostracum δ15N values are reflecting broader North Atlantic hydrographic changes. Our study introduces a new, high-resolution, and absolutely dated paleoceanographic proxy of baseline δ15N values, presenting the opportunity for future reconstructions of aspects of nitrogen cycling and water source changes in the global oceans.
- Published
- 2019
19. DO DIFFERENT BIVALVE MOLLUSK SPECIES RECORD THEIR SHARED ENVIRONMENT IN THE SAME WAY?
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David H. Goodwin, Drew Nederveld, Alan D. Wanamaker, David P. Gillikin, and Anouk Verheyden
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Shared environment ,Ecology ,Bivalve mollusk ,Biology - Published
- 2021
20. Linking the karst record to atmospheric, precipitation, and vegetation dynamics in Portugal
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Jonathan Haws, Frederico Tátá Regala, Alan D. Wanamaker, Alaina G. Chormann, Diana L. Thatcher, Nuno Jorge, Rhawn F. Denniston, Caroline C. Ummenhofer, and David P. Gillikin
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Geochemistry & Geophysics ,010504 meteorology & atmospheric sciences ,δ18O ,Speleothem ,Karst ,Stalagmite ,Precipitation ,010502 geochemistry & geophysics ,01 natural sciences ,Isotopic signature ,Cave ,Isotopes ,Geochemistry and Petrology ,0105 earth and related environmental sciences ,geography ,geography.geographical_feature_category ,Vegetation ,Portugal ,Geology ,Cave monitoring ,North Atlantic oscillation ,NAO ,Physical geography ,Azores High - Abstract
Cave deposits can be valuable sources of paleoclimate data, especially when atmospheric circulation patterns, precipitation variability, vegetation changes, and the chemical evolution of waters moving through the karst environment can be mechanistically linked to speleothem proxies. In particular, an evaluation of the factors that control the isotopic composition of precipitation and the evolution of rainwater during migration from the land surface to the cave are needed to robustly develop speleothems as hydroclimate-sensitive proxies. One area in which precipitation and atmospheric variability are closely linked is western Iberia, where rainfall is strongly influenced by the Azores High, part of the North Atlantic Oscillation (NAO) dipole. Therefore, in order to better characterize the factors that influence the isotopic composition of precipitation in Portugal and to evaluate the potential of using stalagmites from this region as hydroclimate (and NAO-sensitive) proxies, we investigated Global Network of Isotopes in Precipitation (GNIP) data from ten mainland Portugal sites spanning multiple decades. In addition, we use more than one hydrologic year of precipitation amount and isotope data from Buraca Gloriosa (BG), a cave in western Portugal, the site of on-going speleothem analyses, as well as six years of environmental monitoring from BG. We present an integrated analysis of rainfall and vegetation through the normalized difference vegetation index (NDVI) following extremely wet and dry winters. Summer vegetation density, related to the amount of precipitation in the preceding winter wet season, as well as prior calcite precipitation (PCP), would largely control the stable carbon isotopic signature (delta C-13) in stalagmites at BG. Cool season recharge is likely the dominant factor for the oxygen isotopic composition (delta O-18) of water percolating through the cave system, while amount effects exert the primary control on precipitation delta O-18 values. Based on HYSPLIT modeling, moisture sources overwhelmingly originate from the Atlantic Ocean as opposed to the Mediterranean or elsewhere thus, variability in delta O-18 values in the precipitation (and, thus, by inference, those of the dripwater and stalagmites) are primarily reflecting changes in precipitation amount and not changing temperatures or source regions. Together these data constitute an important analysis of the controls of isotope proxies in Portuguese cave systems. US National Science FoundationNational Science Foundation (NSF) [1804528, 1804635, 1804132, 1805163] info:eu-repo/semantics/publishedVersion
- Published
- 2020
21. A 250‐Year, Decadally Resolved, Radiocarbon Time History in the Gulf of Maine Reveals a Hydrographic Regime Shift at the End of the Little Ice Age
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Karl J. Kreutz, Alan D. Wanamaker, Erin E. Lower-Spies, Shelly M. Griffin, Douglas S. Introne, and Nina M. Whitney
- Subjects
Water mass ,Ocean current ,Oceanography ,Proxy (climate) ,law.invention ,Geophysics ,Time history ,Space and Planetary Science ,Geochemistry and Petrology ,law ,Earth and Planetary Sciences (miscellaneous) ,Regime shift ,Radiocarbon dating ,Hydrography ,Little ice age ,Geology - Published
- 2020
22. Variability of the Azores High and regional hydroclimate over the past millennium
- Author
-
Alan D. Wanamaker, Diana L. Thatcher, Rhawn F. Denniston, Caroline C. Ummenhofer, and Nathaniel Cresswell-Clay
- Subjects
Geography ,Climatology ,Azores High - Abstract
The subtropical dry zones, including the broader Mediterranean region, are likely to experience considerable changes in hydroclimate in a warming climate. An expansion of the atmosphere’s meridional overturning circulation, the Hadley circulation, over recent decades has been reported, with implications for regional hydroclimate. Yet, there exists considerable disagreement in magnitude and even sign of these trends among different metrics that measure various aspects of the Hadley circulation, as well as discrepancies in trends between different analysis periods and reanalysis products during the 20th century. In light of these uncertainties, it is therefore of interest to explore variability and trends in subtropical hydroclimate and its dominant driver, the Hadley Circulation. We focus on the North Atlantic sector and explore variability in the Azores High, the manifestation of the Hadley Circulation’s downward branch, and hydroclimate across the Iberian Peninsula using a combination of observational/reanalysis products, state-of-the-art climate model simulations, and hydroclimatically-sensitive stalagmite records over the past 1200 yr. The Last Millennium Ensemble (LME) with the Community Earth System Model provides thirteen transient simulations covering the period 850 to 2005 A.D. with prescribed external forcing (e.g. greenhouse gas, solar, volcanic, land use, orbital, and aerosol) and smaller subsets with individual forcing only. The LME is shown to accurately simulate the variability and trends in the Azores High when compared to observational records from the 20th century. We evaluate variability in the Azores High (e.g., size, intensity, position) in relation to other key metrics that measure different aspects of the Hadley circulation throughout the course of the last millennium, as well as during key periods, such as the Little Ice Age or Medieval Climate Anomaly. The smaller subsets of LME simulations with individual forcing factors (e.g., solar, volcanic) allow for an attribution of past changes in regional hydroclimate to external drivers. Results from the climate model simulations are compared with hydroclimate reconstructed from stalagmites from Portuguese caves.
- Published
- 2020
23. Unprecedented Expansion of the Azores High due to Anthropogenic Climate Change
- Author
-
Rhawn F. Denniston, Caroline C. Ummenhofer, Diana L. Thatcher, Alan D. Wanamaker, and Nathaniel Cresswell-Clay
- Subjects
Oceanography ,Global warming ,Environmental science ,Azores High - Abstract
The Azores High is a subtropical high-pressure ridge in the North Atlantic. During boreal winters, anticyclonic winds rotate around the Azores High, transporting moisture to Western Europe. Variability in the size and intensity of the Azores High thus corresponds to variability in hydroclimate across Western Europe. We use the Last Millennium Ensemble (LME), which is run using the Community Earth System Model (CESM) and features thirteen transient simulations covering the period 850 to 2005 A.D. with prescribed external forcing (e.g. greenhouse gas, solar, volcanic, land use, orbital, and aerosol). The LME is shown to accurately simulate the variability and trends in the Azores High when compared to observational records from the 20th century. The Azores High has grown in size during the Industrial Era. This growth is most dramatic when observing the frequency of winters during which the Azores High is extremely large. The LME shows more winters with an extremely large Azores High in the past 100 years than any other 100-year period in the last millennium. Using LME as well as other simulations from the Paleoclimate Modelling Intercomparison Project Phase III, the recent expansion of the Azores High is shown to be well outside the range of natural variability since 850 A.D. Individual forcing simulations within the LME provide smaller ensembles in which only one external forcing is varied. These experiments attribute Azores High expansion to the recent increase in atmospheric greenhouse gas concentrations. Recent hydroclimatic signals across Western Europe consistent with the Azores High variability are also discussed.
- Published
- 2020
24. Life histories and niche dynamics in late Quaternary proboscideans from Midwestern North America: evidence from stable isotope analyses
- Author
-
Jeffrey J. Saunders, J. Douglas Walker, Alan D. Wanamaker, Greg Hodgins, Chris Widga, Stacey Lengyel, and Kayla Kolis
- Subjects
010506 paleontology ,education.field_of_study ,Extinction ,010504 meteorology & atmospheric sciences ,biology ,Ecology ,Stable isotope ratio ,Population ,15. Life on land ,biology.organism_classification ,01 natural sciences ,Megafauna ,Interglacial ,Glacial period ,education ,Quaternary ,Geology ,0105 earth and related environmental sciences ,Mammoth - Abstract
Stable isotopes of mammoths and mastodons have the potential to illuminate ecological changes in late Pleistocene landscapes and megafaunal populations as these species approached extinction. The ecological factors at play in this extinction remain unresolved, but isotopes of bone collagen (δ13C, δ15N) and tooth enamel (δ13C, δ18O, 87Sr/86Sr) from the Midwest, USA are leveraged to examine ecological and behavioral changes that occurred during the last interglacial-glacial cycle. Both species had significant C3 contributions to their diets and experienced increasing levels of niche overlap as they approached extinction. A subset of mastodons after the last glacial maximum (LGM) exhibit low δ15N values that may represent expansion into a novel ecological niche, perhaps densely occupied by other herbivores. Stable isotopes from serial and micro-sampled enamel show increasing seasonality and decreasing temperatures as mammoths transitioned from Marine Isotope Stage (MIS) 5e to glacial conditions (MIS 4, MIS 3, MIS 2). Isotopic variability in enamel suggests mobility patterns and life histories have potentially large impacts on the interpretation of their stable isotope ecology. This study further refines the ecology of midwestern mammoths and mastodons demonstrating increasing seasonality and niche overlap as they responded to landscape changes in the final millennia before extinction.
- Published
- 2020
25. Pacific climate influences on ocean conditions and extreme shell growth events in the Northwestern Atlantic (Gulf of Maine)
- Author
-
Rhys Parfitt, Nina M. Whitney, Shelly M. Griffin, Alan D. Wanamaker, Karl J. Kreutz, Erin E. Lower-Spies, Bryan A. Black, Caroline C. Ummenhofer, and Douglas S. Introne
- Subjects
Atmospheric Science ,010504 meteorology & atmospheric sciences ,biology ,Atmospheric circulation ,010502 geochemistry & geophysics ,biology.organism_classification ,01 natural sciences ,Sea surface temperature ,Stratification (seeds) ,13. Climate action ,Climatology ,Sclerochronology ,Environmental science ,14. Life underwater ,Hydrography ,Arctica islandica ,Pacific decadal oscillation ,0105 earth and related environmental sciences ,Teleconnection - Abstract
The Gulf of Maine is undergoing rapid environmental and ecological changes, yet our spatial and temporal understanding of the climatic and hydrographic variability in this region, including extreme events, is limited and biased to recent decades. In this study, we utilize a highly replicated, multi-century master shell growth chronology derived from the annual increments formed in the shells of the long-lived bivalve Arctica islandica collected in 38 m from the central coastal region in the Gulf of Maine. Our results indicate that shell growth is highly synchronous and inversely related to local seawater temperatures. Using composite analyses of extreme shell growth events from CE 1900 to 2013, we extend our understanding of the factors driving oceanic variability and shell growth in the Northwestern Atlantic back to CE 1761. We suggest that extreme shell growth events are primarily controlled by Gulf of Maine sea surface temperature (SST) and stratification conditions, which in turn appear to be largely influenced by SST patterns in the Pacific Ocean through their influence on mid-latitude atmospheric circulation patterns and the location of the eddy-driven jet. The large-scale jet dynamics during these extreme years manifest as precipitation and moisture transport anomalies and regional SST conditions in the Gulf of Maine that either enhance or inhibit shell growth. Pacific climate variability is thus an important, yet understudied, influence on Gulf of Maine ocean conditions.
- Published
- 2018
26. Unexpected isotopic variability in biogenic aragonite: A user issue or proxy problem?
- Author
-
Nina M. Whitney, Madelyn J. Mette, Jared Ballew, and Alan D. Wanamaker
- Subjects
education.field_of_study ,010504 meteorology & atmospheric sciences ,δ13C ,δ18O ,Aragonite ,Population ,Sampling (statistics) ,Geology ,Replicate ,engineering.material ,010502 geochemistry & geophysics ,Atmospheric sciences ,01 natural sciences ,Isotopes of oxygen ,13. Climate action ,Geochemistry and Petrology ,engineering ,14. Life underwater ,education ,Transect ,0105 earth and related environmental sciences - Abstract
The present study seeks to investigate sources of isotopic variability in the commonly used paleoclimate archive, the marine bivalve Arctica islandica, with an emphasis on the potential of human-induced variability arising from sampling techniques. Stable carbon (δ13Ccarbonate) and oxygen (δ18Ocarbonate) isotopes were analyzed for split (intra-sample) and replicate (intra- and inter-shell) samples taken from a group of laboratory-reared individuals, a natural population from northern Norway, and a natural population from the Gulf of Maine, USA. Compared to analytical uncertainty of 0.17‰ and 0.30‰ for δ13C and δ18O, respectively, among the natural populations, the mean difference between shell splits and shell replicates ranged from 0.12‰ and 0.33‰ for δ13C and δ18O, respectively. Our data suggest that heterogeneity of the carbonate material (i.e., large range of isotopic composition within one sample due to seasonal environmental variability) may contribute to “unexpected” variability more than human-induced error from sampling imprecision when collecting whole annual increments. Furthermore, δ13C from juvenile shells were highly variable (2σ standard deviation = 0.65‰), approximately four times more variable than analytical precision. High precision among δ18O measurements of the laboratory-reared shells confirm the presumption that shells reliably and consistently precipitate in isotopic equilibrium with ambient seawater. Monte Carlo simulations of measurements from this population allowed characterization of improvements in uncertainty at increasing levels of replication. Substantial reduction in uncertainty occurs when increasing from two to three shells, however replication using a total of four shells further decreased uncertainty to within the 99% confidence level. Published studies sometimes compensate for uncertainties by replicating records over multiple individuals or multiple transects within the one individual. Oftentimes, however, isotope records are constructed from single individuals or transects and therefore fail to provide thorough estimates of proxy error. Our findings suggest that replication of carbon and oxygen isotope measurements of contemporaneously produced aragonite is necessary in order to reduce proxy-derived noise. Furthermore, population-specific estimates of uncertainty related to natural variability among individuals should be investigated in order to provide more realistic representations of proxy noise when reporting isotope time series.
- Published
- 2018
27. Biological and Climate Controls on North Atlantic Marine Carbon Dynamics Over the Last Millennium: Insights From an Absolutely Dated Shell-Based Record From the North Icelandic Shelf
- Author
-
Christopher A. Richardson, Ian Hall, James D. Scourse, David J. Reynolds, Alan D. Wanamaker, and Paul G. Butler
- Subjects
010506 paleontology ,Atmospheric Science ,Global and Planetary Change ,Carbon dioxide in Earth's atmosphere ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,biology ,Atmospheric carbon cycle ,biology.organism_classification ,01 natural sciences ,Carbon cycle ,Suess effect ,Sea surface temperature ,Oceanography ,North Atlantic oscillation ,Ocean gyre ,Environmental Chemistry ,Arctica islandica ,Geology ,0105 earth and related environmental sciences ,General Environmental Science - Abstract
Given the rapid increase in atmospheric carbon dioxide concentrations (pCO2) over the industrial era, there is a pressing need to construct long‐term records of natural carbon cycling prior to this perturbation and to develop a more robust understanding of the role the oceans play in the sequestration of atmospheric carbon. Here we reconstruct the past biological and climate controls on the carbon isotopic (δ13Cshell) composition of the North Icelandic shelf waters over the last millennium, derived from the shells of the long‐lived marine bivalve mollusk Arctica islandica. Variability in the annually resolved δ13Cshell record is dominated by multidecadal variability with a negative trend (−0.003 ± 0.002‰ yr−1) over the industrial era (1800–2000 Common Era). This trend is consistent with the marine Suess effect brought about by the sequestration of isotopically light carbon (δ13C of CO2) derived from the burning of fossil fuels. Comparison of the δ13Cshell record with Contemporaneous proxy archives, over the last millennium, and instrumental data over the twentieth century, highlights that both biological (primary production) and physical environmental factors, such as relative shifts in the proportion of Subpolar Mode Waters and Arctic Intermediate Waters entrained onto the North Icelandic shelf, atmospheric circulation patterns associated with the winter North Atlantic Oscillation, and sea surface temperature and salinity of the subpolar gyre, are the likely mechanisms that contribute to natural variations in seawater δ13C variability on the North Icelandic shelf. Contrasting δ13C fractionation processes associated with these biological and physical mechanisms likely cause the attenuated marine Suess effect signal at this locality.
- Published
- 2017
28. Decoupling of monsoon activity across the northern and southern Indo-Pacific during the Late Glacial
- Author
-
Stephanie Lucker, Alan D. Wanamaker, Yemane Asmerom, Rhawn F. Denniston, Caroline C. Ummenhofer, William F. Humphreys, John Cugley, David Woods, and Victor J. Polyak
- Subjects
Archeology ,Global and Planetary Change ,010504 meteorology & atmospheric sciences ,Intertropical Convergence Zone ,Northern Hemisphere ,Geology ,010502 geochemistry & geophysics ,Monsoon ,01 natural sciences ,Oceanography ,Pluvial ,Climatology ,Glacial period ,Stadial ,Precipitation ,Ecology, Evolution, Behavior and Systematics ,Holocene ,0105 earth and related environmental sciences - Abstract
Recent studies of stalagmites from the Southern Hemisphere tropics of Indonesia reveal two shifts in monsoon activity not apparent in records from the Northern Hemisphere sectors of the Austral-Asian monsoon system: an interval of enhanced rainfall at ∼19 ka, immediately prior to Heinrich Stadial 1, and a sharp increase in precipitation at ∼9 ka. Determining whether these events are site-specific or regional is important for understanding the full range of sensitivities of the Austral-Asian monsoon. We present a discontinuous 40 kyr carbon isotope record of stalagmites from two caves in the Kimberley region of the north-central Australian tropics. Heinrich stadials are represented by pronounced negative carbon isotopic anomalies, indicative of enhanced rainfall associated with a southward shift of the intertropical convergence zone and consistent with hydroclimatic changes observed across Asia and the Indo-Pacific. Between 20 and 8 ka, however, the Kimberley stalagmites, like the Indonesian record, reveal decoupling of monsoon behavior from Southeast Asia, including the early deglacial wet period (which we term the Late Glacial Pluvial) and the abrupt strengthening of early Holocene monsoon rainfall.
- Published
- 2017
29. Reproducibility of trace element time-series (Na/Ca, Mg/Ca, Mn/Ca, Sr/Ca, and Ba/Ca) within and between specimens of the bivalve Arctica islandica – A LA-ICP-MS line scan study
- Author
-
Hilmar A. Holland, Alan D. Wanamaker, Paul G. Butler, Klaus Peter Jochum, Soraya Marali, Shelly M. Griffin, Bernd R. Schöne, and Regina Mertz-Kraus
- Subjects
Strontium ,Reproducibility ,010504 meteorology & atmospheric sciences ,biology ,Magnesium ,Sodium ,Trace element ,Paleontology ,chemistry.chemical_element ,Mineralogy ,Barium ,Manganese ,010502 geochemistry & geophysics ,Oceanography ,biology.organism_classification ,01 natural sciences ,chemistry ,Arctica islandica ,Ecology, Evolution, Behavior and Systematics ,Geology ,0105 earth and related environmental sciences ,Earth-Surface Processes - Abstract
Trace element time-series in bivalve mollusk shells and other (biogenic) materials can potentially serve as environmental proxies. Yet, the applicability of element-to-calcium ratios is often challenging, because non-environmental factors such as vital effects distort or mask environmental signals. If a trace element time-series is driven by an environmental factor, it should be reproducible within and between coeval specimens of the same species. In the present study, we tested whether time-series of trace element-to-calcium ratios can be reproduced within and between coeval specimens of the bivalve Arctica islandica and thus whether an external signal is encoded in the temporal variations of trace elements along the shells. We determined the concentration of sodium, magnesium, manganese, strontium and barium by means of LA-ICP-MS in line scan mode in the hinge area of seven specimens from the Isle of Man, the Gulf of Maine and Iceland. In each specimen, the element composition was determined along two replicate line scans to gauge intra-specimen reproducibility. The degree to which trace element time-series can be reproduced was inferred from linear regression analysis and equaled on average 95 ± 4% for Ba/Ca, 82 ± 27% for Mg/Ca, 83 ± 18% for Sr/Ca, 74 ± 23% for Mn/Ca, and 22 ± 4% for Na/Ca ratios (values correspond to coefficients of determination of the linear regression analysis expressed in percent). The synchrony of Ba/Ca time-series between contemporaneous specimens from the same habitat has already been demonstrated in previous studies. Here, we observed common high-frequency variations (i.e., peaks) among coeval A. islandica from the same site for Mg/Ca, Sr/Ca, Mn/Ca and Na/Ca ratios, especially among specimens of similar ontogenetic age and with similar shell growth patterns. The results of the present study should be considered in interpretations of trace element time-series in bivalve shells as they can help to improve environmental and climate reconstructions.
- Published
- 2017
30. Cyanobacterial carbon concentrating mechanisms facilitate sustained CO2 depletion in eutrophic lakes
- Author
-
Alan D. Wanamaker, John A. Downing, and Ana M. Morales-Williams
- Subjects
0106 biological sciences ,Biomass (ecology) ,010504 meteorology & atmospheric sciences ,Ecology ,010604 marine biology & hydrobiology ,Aquatic ecosystem ,fungi ,15. Life on land ,01 natural sciences ,Algal bloom ,Water column ,Total inorganic carbon ,13. Climate action ,Phytoplankton ,Dissolved organic carbon ,Environmental science ,14. Life underwater ,Eutrophication ,Ecology, Evolution, Behavior and Systematics ,0105 earth and related environmental sciences ,Earth-Surface Processes - Abstract
Phytoplankton blooms are increasing in frequency, intensity, and duration in aquatic ecosystems worldwide. In many eutrophic lakes, these high levels of primary productivity correspond to periods of CO2 depletion in surface waters. Cyanobacteria and other groups of phytoplankton have the ability to actively transport bicarbonate (HCO3−) across their cell membrane when CO2 concentrations are limiting, possibly giving them a competitive advantage over algae not using carbon concentrating mechanisms (CCMs). To investigate whether CCMs can maintain phytoplankton bloom biomass under CO2 depletion, we measured the δ13C signatures of dissolved inorganic carbon (δ13CDIC) and phytoplankton particulate organic carbon (δ13Cphyto) in 16 mesotrophic to hypereutrophic lakes during the ice-free season of 2012. We used mass–balance relationships to determine the dominant inorganic carbon species used by phytoplankton under CO2 stress. We found a significant positive relationship between phytoplankton biomass and phytoplankton δ13C signatures as well as a significant nonlinear negative relationship between water column ρCO2 and isotopic composition of phytoplankton, indicating a shift from diffusive uptake to active uptake by phytoplankton of CO2 or HCO3− during blooms. Calculated photosynthetic fractionation factors indicated that this shift occurs specifically when surface water CO2 drops below atmospheric equilibrium. Our results indicate that active HCO3− uptake via CCMs may be an important mechanism in maintaining phytoplankton blooms when CO2 is depleted. Further increases in anthropogenic pressure, eutrophication, and cyanobacteria blooms are therefore expected to contribute to increased bicarbonate uptake to sustain primary production.
- Published
- 2017
31. El Niño–Southern Oscillation–like variability in a late Miocene Caribbean coral
- Author
-
Anna von der Heydt, Thomas L. Weiss, Gabriele Villarini, Alan D. Wanamaker, and Rhawn F. Denniston
- Subjects
Series (stratigraphy) ,010504 meteorology & atmospheric sciences ,Coral ,Central American Seaway ,Geology ,Late Miocene ,010502 geochemistry & geophysics ,01 natural sciences ,Isotopes of oxygen ,La Niña ,Oceanography ,El Niño ,Climatology ,Thermocline ,0105 earth and related environmental sciences - Abstract
Reconstructions of Pliocene sea-surface temperature (SST) gradients and thermocline depths suggest that the zonal temperature gradient of the tropical Pacific was distinct from the modern. However, the nature of any El Nino–Southern Oscillation (ENSO) variability superimposed on this mean state is difficult to determine. We developed monthly resolved multidecadal stable isotopic time series from an extremely well preserved central Caribbean coral dating to the Miocene-Pliocene transition, prior to closure of the Central American Seaway (CAS). Paleoceanographic modeling suggests that the flow of water associated with El Nino and La Nina events through the CAS allowed Caribbean corals to record the ENSO-related SST anomalies. Spectral analysis of coral oxygen isotope ratios reveals periodicities similar to modern ENSO signatures, suggesting that ENSO-like variability characterized the Miocene-Pliocene transition.
- Published
- 2017
32. Spatial and temporal variability in the δ18O and salinity compositions of Gulf of Maine coastal surface waters
- Author
-
Nina M. Whitney, Alan D. Wanamaker, Karl J. Kreutz, and Douglas S. Introne
- Subjects
010504 meteorology & atmospheric sciences ,River runoff ,Baseline (sea) ,Geology ,Aquatic Science ,010502 geochemistry & geophysics ,Oceanography ,01 natural sciences ,River water ,Isotopes of oxygen ,Salinity ,Hydrography ,Surface water ,0105 earth and related environmental sciences - Abstract
Hydrographic variability and dynamics in the Gulf of Maine are examined through the investigation of δ 18 O w and salinity properties of coastal surface waters. Data from Gulf of Maine waters sampled over a decade, from 2003 to 2015, including a suite of samples that were collected monthly from April 2014 to March 2015, are presented. These water samples fall on a mixing line between Maine River Water (MRW) and Scotian Shelf Water (SSW). However, slope waters likely also contribute to these surface waters. The seasonal variability in water samples collected during 2014 and 2015 indicates the strong influence of river runoff on coastal Gulf of Maine surface water properties. The coastal Gulf of Maine mixing line presented in this paper is a needed baseline for reconstructing hydrographic variability in bicarbonates using oxygen isotopes.
- Published
- 2017
33. Late Pleistocene proboscidean population dynamics in the North American Midcontinent
- Author
-
Alan D. Wanamaker, Chris Widga, J. Douglas Walker, Stacey Lengyel, Jeffrey J. Saunders, and Gregory W. L. Hodgins
- Subjects
010506 paleontology ,Archeology ,education.field_of_study ,Extinction ,010504 meteorology & atmospheric sciences ,biology ,Pleistocene ,Ecology ,Population ,Geology ,Last Glacial Maximum ,biology.organism_classification ,01 natural sciences ,Proboscidea ,Megafauna ,Younger Dryas ,education ,Ecology, Evolution, Behavior and Systematics ,0105 earth and related environmental sciences ,Mammoth - Abstract
Understanding megafaunal population dynamics is critical to testing and refining scenarios of how extinctions occurred during the terminal Pleistocene. Large-scale, collections-based, chronological and taphonomic analyses of midwestern Proboscidea suggest divergent population histories in mammoths and mastodons after the Last Glacial Maximum (LGM). Although extinction of both taxa occurred in the very late Bolling-Allerod (B-A) or early Younger Dryas (YD), Mammuthus is dominant during the LGM with a decreasing presence in the region until extirpation. Mammut americanum however, is absent during the LGM but becomes the dominant taxon during the subsequent B-A. Trace and physical evidence of large carnivores in post-LGM proboscidean assemblages is extremely rare, suggesting apex predators had minimal impact on mammoth and mastodon populations at this time. The ultimate mechanism(s) of extinction remain unclear; however, the wide geographical distribution of late Mammut and an increase in the frequency of multi-animal death assemblages is consistent with a large, destabilized population experiencing periodic boom-bust cycling at the end of the B-A. We suggest this pattern is due to the collapse of trophic controls on proboscidean populations prior to the LGM and a subsequent system-wide shift from top-down to bottom-up regulatory mechanisms in Proboscidea.
- Published
- 2017
34. Ba/Ca ratios in shells of Arctica islandica —Potential environmental proxy and crossdating tool
- Author
-
Alan D. Wanamaker, Shelly M. Griffin, Bernd R. Schöne, Soraya Marali, Regina Mertz-Kraus, Una Matras, and Paul G. Butler
- Subjects
education.field_of_study ,010504 meteorology & atmospheric sciences ,biology ,Population ,Paleontology ,Mineralogy ,010502 geochemistry & geophysics ,Oceanography ,biology.organism_classification ,01 natural sciences ,Salinity ,Time averaging ,Sampling resolution ,Causal link ,Bivalve shell ,education ,Arctica islandica ,Ecology, Evolution, Behavior and Systematics ,Primary productivity ,Geology ,0105 earth and related environmental sciences ,Earth-Surface Processes - Abstract
Ba/Ca shell time-series of marine bivalves typically show flat background levels which are interrupted by erratic sharp peaks. Evidence from the literature indicates that background Ba/Ca shell ratios broadly reflect salinity conditions. However, the causes for the Ba/Ca shell peaks are still controversial and widely debated although many researchers link these changes to primary productivity, freshwater input or spawning events. The most striking feature is that the Ba/Ca shell peaks are highly synchronous in contemporaneous specimens from the same population. For the first time, we studied Ba/Ca shell in mature and ontogenetically old (up to 251 year-old) specimens of the long-lived Arctica islandica . Also, we analyzed specimens from surface water and deeper water. The typical pattern of low background and erratic peaks persisted throughout ontogeny. However, due to decreasing sampling resolution and greater time-averaging in older, slower growing shell portions, the background Ba/Ca shell values appeared to gradually increase with ontogenetic age, whereas the peaks became attenuated and broader. Despite that, Ba/Ca shell maxima were still highly synchronous among contemporaneous specimens from the same locality and habitat confirming previous reports from short-lived species. Computing of annual Ba/Ca shell averages largely eliminated any bias introduced by time-averaging and sampling resolution. Strongly elevated annual Ba/Ca shell peaks in specimens from surface waters (Iceland, Faroe Islands, Isle of Man) during the 1980s appear to coincide with an extreme primary productivity pulse recorded by remote sensing. However, due to the lack of in vivo experiments, we cannot ultimately test a causal link between annual Ba/Ca shell excursions and primary productivity. We propose that Ba/Ca shell time-series, specifically the highly synchronous Ba/Ca shell peaks and annual Ba/Ca shell values in contemporaneous specimens from the same locality can serve as a tool to verify crossdating and facilitate the construction of statistically robust growth increment width master chronologies. Long-term environmental reconstructions based on bivalve shell growth chronologies can likely greatly benefit from this new technique.
- Published
- 2017
35. The revolution of crossdating in marine palaeoecology and palaeoclimatology
- Author
-
Bernd R. Schöne, Alan D. Wanamaker, James D. Scourse, Peter van der Sleen, Rob Witbaard, Paul G. Butler, Michael L. Carroll, Carin Andersson, Bryan A. Black, Kristine L. DeLong, and David J. Reynolds
- Subjects
0106 biological sciences ,010504 meteorology & atmospheric sciences ,010604 marine biology & hydrobiology ,Climate ,Climate Change ,Oceans and Seas ,Climate change ,Global Change Biology ,Biology ,01 natural sciences ,Agricultural and Biological Sciences (miscellaneous) ,Trees ,Paleoceanography ,Sclerochronology ,Paleoclimatology ,Paleoecology ,Dendrochronology ,Animals ,Physical geography ,General Agricultural and Biological Sciences ,Ecosystem ,0105 earth and related environmental sciences - Abstract
Over the past century, the dendrochronology technique of crossdating has been widely used to generate a global network of tree-ring chronologies that serves as a leading indicator of environmental variability and change. Only recently, however, has this same approach been applied to growth increments in calcified structures of bivalves, fish and corals in the world's oceans. As in trees, these crossdated marine chronologies are well replicated, annually resolved and absolutely dated, providing uninterrupted multi-decadal to millennial histories of ocean palaeoclimatic and palaeoecological processes. Moreover, they span an extensive geographical range, multiple trophic levels, habitats and functional types, and can be readily integrated with observational physical or biological records. Increment width is the most commonly measured parameter and reflects growth or productivity, though isotopic and elemental composition capture complementary aspects of environmental variability. As such, crossdated marine chronologies constitute powerful observational templates to establish climate–biology relationships, test hypotheses of ecosystem functioning, conduct multi-proxy reconstructions, provide constraints for numerical climate models, and evaluate the precise timing and nature of ocean–atmosphere interactions. These ‘present–past–future’ perspectives provide new insights into the mechanisms and feedbacks between the atmosphere and marine systems while providing indicators relevant to ecosystem-based approaches of fisheries management.
- Published
- 2019
36. CALIBRATING HYDROCLIMATE PROXIES IN TWO SOUTHERN PORTUGUESE SPELEOTHEMS
- Author
-
Diana L. Thatcher, Victor J. Polyak, Alan D. Wanamaker, Yemane Asmerom, David P. Gillikin, and Alaina G. Chormann
- Subjects
Physical geography - Published
- 2019
37. A STALAGMITE COMPOSITE RECORD OF HYDROCLIMATE VARIABILITY FROM PORTUGAL DURING THE HOLOCENE
- Author
-
Daniel Fullick, Victor J. Polyak, Rhawn F. Denniston, Caroline C. Ummenhofer, Yemane Asmerom, David P. Gillikin, Diana L. Thatcher, Alan D. Wanamaker, and Jonathan Haws
- Subjects
geography ,geography.geographical_feature_category ,Stalagmite ,Physical geography ,Holocene ,Geology - Published
- 2019
38. A MULTI-SPECIES SURVEY OF NITROGEN ISOTOPES IN MARINE MOLLUSK SOFT TISSUES FROM A NORTH CAROLINA COASTAL SYSTEM: AN INDICATOR OF ANTHROPOGENIC NITROGEN LOADING?
- Author
-
Alan D. Wanamaker, Hayley I. Bennett, Emily Carrigan, David P. Gillikin, Elizabeth Cilia, Heidi O'Hora, Mihai Fratian, and David H. Goodwin
- Subjects
chemistry ,Environmental chemistry ,Multi species ,Environmental science ,chemistry.chemical_element ,Nitrogen ,Isotopes of nitrogen - Published
- 2019
39. CLAMS AND OYSTERS—APPLES AND ORANGES? COMPARING CONTEMPORARY BIOGEOCHEMICAL ARCHIVES FROM MERCENARIA MEARCENARIA AND CRASSOSTREA VIRGINICA
- Author
-
Alan D. Wanamaker, David H. Goodwin, Eva Nur Jorn, and David P. Gillikin
- Subjects
Fishery ,Biogeochemical cycle ,Mercenaria ,biology ,Crassostrea ,biology.organism_classification - Published
- 2019
40. CARBON DYNAMICS IN A MARSH-DOMINATED ESTUARINE SYSTEM
- Author
-
Emily Carrigan, Heidi O'Hora, Mihai Fratian, Hayley I. Bennett, David P. Gillikin, Alan D. Wanamaker, Elizabeth Cilia, and David H. Goodwin
- Subjects
geography ,Marsh ,geography.geographical_feature_category ,Oceanography ,chemistry ,Environmental science ,chemistry.chemical_element ,Estuary ,Carbon - Published
- 2019
41. INTERTROPICAL CONVERGENCE ZONE DYNAMICS AND NORTHERN SOUTH AMERICA RAINFALL VARIABILITY DURING THE LAST 50 KYRS FROM COLOMBIAN STALAGMITES
- Author
-
Victor J. Polyak, Alan D. Wanamaker, Karine L. Holmes, Juan Carlos Romero Gelvez, Yemane Asmerom, and Diana L. Thatcher
- Subjects
geography ,geography.geographical_feature_category ,Climatology ,Intertropical Convergence Zone ,Stalagmite ,Geology - Published
- 2019
42. ENVIRONMENTAL SIGNALS FROM DONAX OBESULUS PROVIDE INFORMATION ON EL NIÑO-SOUTHERN OSCILLATION (ENSO) VARIABILITY
- Author
-
Kristine L. DeLong, Alan D. Wanamaker, J. Warner, Kaustubh Thirumalai, C. Fred T. Andrus, and David Chicoine
- Subjects
Oceanography ,El Niño Southern Oscillation ,Environmental science ,Donax obesulus - Published
- 2019
43. Comparing contemporary biogeochemical archives from Mercenaria mercenaria and Crassostrea virginica: Insights on paleoenvironmental reconstructions
- Author
-
Mihai Fratian, Eva Nur Jorn, David P. Gillikin, David H. Goodwin, and Alan D. Wanamaker
- Subjects
Calcite ,Biogeochemical cycle ,Mercenaria ,biology ,δ18O ,Aragonite ,Paleontology ,engineering.material ,Oceanography ,biology.organism_classification ,Isotopes of oxygen ,chemistry.chemical_compound ,chemistry ,engineering ,Carbonate ,Crassostrea ,Ecology, Evolution, Behavior and Systematics ,Geology ,Earth-Surface Processes - Abstract
Reconstruction of past environmental conditions from modern and fossil organisms is predicated on predictable biological responses to environmental variation. Thus, understanding how different species record commonly experienced environmental conditions is critical. This is particularly important in settings where multiple biogeochemical archives are available for study (e.g., a species rich fossil assemblage). Previous work has documented species-specific thermal tolerances and growth rates, which suggests proxy-based reconstructions may reflect a combination of biological controls and environmental variation. To investigate this potential complication, we compared oxygen isotope (δ18O) profiles from shells of two contemporary marine bivalve mollusks (Mercenaria mercenaria and Crassostrea virginica) growing in the same locality (Cape Lookout region, North Carolina, USA). Carbonate oxygen isotope samples (δ18Oc) were collected from shell material deposited between August 2016 and April 2019. These data were calibrated with predicted δ18Oc profiles (aragonite and calcite) calculated from high resolution environmental records (hourly temperature records and weekly water samples). M. mercenaria specimens were periodically stained with calcein during the study interval, facilitating transformation of the δ18Oc profiles into the time domain. δ18Oc profiles from C. virginica were fit directly to the predicted δ18Oc profile. Our results suggest that M. mercenaria and C. virginica living in the Cape Lookout region are capable of depositing shell material throughout the year. Shell growth in both species slows significantly, or halts altogether, during short term large magnitude freshwater input events. M. mercenaria examined in this study show a strong preference for growth during the warmest hours of the day. This observation suggests optimal growth temperatures lie close to the upper limit of temperatures recorded at the study site. C. virginica does not show a preference for shell growth during the warm or cold hours of the day. Thus, a major conclusion of this study is that two different species living in the same place at the same time may record different aspects of commonly experienced environmental conditions. Nevertheless, our findings suggest the fossil record may contain more detailed archives of past environmental conditions than previously thought. Future studies should focus on high-resolution, short-duration calibrations where environmental data is recorded at the time, location, and resolution.
- Published
- 2021
44. Using stable isotopes as tracers of water masses and nutrient cycling processes in the Gulf of Maine
- Author
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Nina M. Whitney, Neal R. Pettigrew, Megan E. Switzer, and Alan D. Wanamaker
- Subjects
0106 biological sciences ,Water mass ,010504 meteorology & atmospheric sciences ,Stable isotope ratio ,010604 marine biology & hydrobiology ,Geology ,Aquatic Science ,Oceanography ,01 natural sciences ,Isotopes of oxygen ,Salinity ,Box modeling ,Water column ,Phytoplankton ,Environmental science ,Hydrography ,0105 earth and related environmental sciences - Abstract
The dramatic marine environmental change seen today can be difficult to fully document and interpret without adequate, spatially and temporally comprehensive, baseline datasets of hydrographic properties. Here we present isotope data measured in water samples collected during a nine-day research cruise in October 2016 throughout the Gulf of Maine, a rapidly changing region of the world's oceans. A comparison of the oxygen isotopes of the water (δ18Owater) and salinity data reveal that water samples fall on a tight, linear mixing line between fresher shelf water and saltier slope waters, with the freshwater endmember originating from much higher latitudes (the Gulf of St. Lawrence and the Labrador Sea). Some subtle differences in freshwater endmembers are observed between the three different deep basins in the Gulf of Maine. These differences are likely reflecting differences in freshwater input and vertical mixing between the different basins. Additionally, these water samples have lower δ18Owater values for a given salinity value than previously published values of marine water mass endmembers. This offset may be related to systematic changesin water mass endmember values or year to year variability, as well as differences in the proportions of water masses entering the Gulf of Maine. Nitrogen and oxygen isotopes of dissolved nitrate (NO3−; δ15NNO3- and δ18ONO3-, respectively) measured in the water samples suggest a strong influence of phytoplankton assimilation near the surface in both isotopic systems. Combining these two datasets using Δ(15, 18) to look at the rates of fractionation between the two isotope systems reveals potential water column nitrification above 100 m in most places in the Gulf of Maine. This finding provides support for previous hypotheses of water column nitrification in the Gulf of Maine based on nutrient distribution and nitrogen box modeling. However, these calculations rely on the assumption that all nitrate is sourced from deeper waters. It is possible these results are instead caused by NO3− from different sources at the surface and therefore do not necessarily indicate the presence of nitrification.
- Published
- 2020
45. The value of crossdating to retain high‐frequency variability, climate signals, and extreme events in environmental proxies
- Author
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David Frank, Alan D. Wanamaker, Valerie Trouet, David W. Stahle, Shelly M. Griffin, Peter van der Sleen, Carolyn A. Copenheaver, Neil Pederson, Daniel Griffin, James H. Speer, Bronwyn M. Gillanders, and Bryan A. Black
- Subjects
0106 biological sciences ,010504 meteorology & atmospheric sciences ,Climate ,Fresh Water ,01 natural sciences ,Natural (archaeology) ,Trees ,Sclerochronology ,Paleoclimatology ,Dendrochronology ,Animals ,Environmental Chemistry ,0105 earth and related environmental sciences ,General Environmental Science ,Global and Planetary Change ,Ecology ,010604 marine biology & hydrobiology ,Fishes ,Extreme events ,Global change ,500 Science ,Bivalvia ,Climatology ,Environmental science ,Tree species ,Value (mathematics) - Abstract
High-resolution biogenic and geologic proxies in which one increment or layer is formed per year are crucial to describing natural ranges of environmental variability in Earth's physical and biological systems. However, dating controls are necessary to ensure temporal precision and accuracy; simple counts cannot ensure that all layers are placed correctly in time. Originally developed for tree-ring data, crossdating is the only such procedure that ensures all increments have been assigned the correct calendar year of formation. Here, we use growth-increment data from two tree species, two marine bivalve species, and a marine fish species to illustrate sensitivity of environmental signals to modest dating error rates. When falsely added or missed increments are induced at one and five percent rates, errors propagate back through time and eliminate high-frequency variability, climate signals, and evidence of extreme events while incorrectly dating and distorting major disturbances or other low-frequency processes. Our consecutive Monte Carlo experiments show that inaccuracies begin to accumulate in as little as two decades and can remove all but decadal-scale processes after as little as two centuries. Real-world scenarios may have even greater consequence in the absence of crossdating. Given this sensitivity to signal loss, the fundamental tenets of crossdating must be applied to fully resolve environmental signals, a point we underscore as the frontiers of growth-increment analysis continue to expand into tropical, freshwater, and marine environments.
- Published
- 2016
46. Linking large-scale climate variability with A rctica islandica shell growth and geochemistry in northern Norway
- Author
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Michael J. Retelle, William G. Ambrose, Michael L. Carroll, Alan D. Wanamaker, and Madelyn J. Mette
- Subjects
010504 meteorology & atmospheric sciences ,biology ,δ18O ,Aquatic Science ,010502 geochemistry & geophysics ,Oceanography ,biology.organism_classification ,01 natural sciences ,Sea surface temperature ,Arctic ,North Atlantic oscillation ,Paleoclimatology ,Atlantic multidecadal oscillation ,Hydrography ,Arctica islandica ,Geology ,0105 earth and related environmental sciences - Abstract
The lack of high resolution, geographically diverse proxy records from the marine realm limits our understanding of climate dynamics in the North Atlantic Ocean and Arctic during recent centuries. We investigate the impact of large-scale climate variability on the marine bivalve, Arctica islandica, (Linnaeus 1767) from northern Norway (71°N). We evaluate the use of annual shell growth and geochemical records as proxies for North Atlantic and Arctic climate variability over centennial scales by developing a continuous, 113-yr master shell growth chronology and an oxygen isotope record (δ18O) from live caught shell material. A relatively strong inverse relationship is observed between both the shell growth and isotopic proxies and large-scale North Atlantic sea surface temperatures in modern times (r = −0.54 to −0.90; p
- Published
- 2015
47. Divergent responses of spring phenology to daytime and nighttime warming
- Author
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Jiafu Mao, Ghasserm R. Asrar, Alan D. Wanamaker, Lin Meng, Yuyu Zhou, Yeqiao Wang, and Xuecao Li
- Subjects
0106 biological sciences ,Atmospheric Science ,Global and Planetary Change ,Daytime ,Maximum temperature ,010504 meteorology & atmospheric sciences ,Phenology ,Forestry ,Spring (mathematics) ,Atmospheric sciences ,01 natural sciences ,Partial correlation analysis ,Diurnal warming ,Temperate climate ,Environmental science ,Agronomy and Crop Science ,Partial correlation ,010606 plant biology & botany ,0105 earth and related environmental sciences - Abstract
Spring phenology (i.e., start of season, SOS) of plants in temperate regions has shifted earlier in response to increasing temperature. However, the respective influences of daytime and nighttime warming on the changes in SOS remain poorly understood although an ongoing asymmetric diurnal warming has been observed. In this study, we characterized the responses of satellite-derived SOS to daily minimum temperature (Tmin) and maximum temperature (Tmax) across Appalachian Trail regions in the Eastern United States between 2001 and 2013 using a partial correlation analysis. We found that the partial correlation coefficients between SOS and T m i n ( R S O S − T m i n ) are opposite in sign compared to that between SOS and T m a x ( R S O S − T m a x ) in 81.5% of study area. Furthermore, we found a significant decrease in R S O S − T m i n and an increase in R S O S − T m a x from cold to warm regions (P
- Published
- 2020
48. Isolating and reconstructing key components of North Atlantic Ocean variability from a sclerochronological spatial network
- Author
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Ian Hall, David J. Reynolds, James D. Scourse, Alan D. Wanamaker, Madelyn J. Mette, Paul R. Halloran, Freya Garry, and Sophie M. Slater
- Subjects
010506 paleontology ,Atmospheric Science ,Series (stratigraphy) ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Baseline (sea) ,Paleontology ,Tropical Atlantic ,Oceanography ,01 natural sciences ,Salinity ,13. Climate action ,Absolute dating ,Ocean gyre ,Sclerochronology ,Period (geology) ,Environmental science ,14. Life underwater ,0105 earth and related environmental sciences - Abstract
Our understanding of North Atlantic Ocean variability within the coupled climate system is limited by the brevity of instrumental records and a deficiency of absolutely dated marine proxies. Here we demonstrate that a spatial network of marine stable oxygen isotope series derived from molluscan sclerochronologies (δ18Oshell) can provide skillful annually resolved reconstructions of key components of North Atlantic Ocean variability with absolute dating precision. Analyses of the common δ18Oshell variability, using principal component analyses (PCA), highlight strong connections with tropical North Atlantic and subpolar gyre (SPG) sea surface temperatures (SSTs) and sea surface salinity (SSS) in the North Atlantic Current (NAC) region. These analyses suggest that low frequency variability is dominated by the tropical Atlantic signal whilst decadal variability is dominated by variability in the SPG and salinity transport in the NAC. Split calibration and verification statistics indicate that the composite series produced using the PCA can provide skillful quantitative reconstructions of tropical North Atlantic and SPG SSTs and NAC SSSs over the industrial period (1864‐2000). The application of these techniques with extended individual δ18Oshell series provide powerful baseline records of past North Atlantic variability into the unobserved pre‐industrial period. Such records are essential for developing our understanding of natural climate variability in the North Atlantic Ocean and the role it plays in the wider climate system, especially on multi‐decadal to centennial timescales, potentially enabling reduction of uncertainties in future climate predictions.
- Published
- 2018
49. STALAGMITE RECORDS FROM WEST-CENTRAL PORTUGAL TEST LINKS BETWEEN NORTH ATLANTIC PALEOCEANOGRAPHY AND IBERIAN CONTINENTAL CLIMATE OVER THE PAST TWO GLACIAL CYCLES
- Author
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Setsen Altan-Ochir, Jonathan Haws, Yemane Asmerom, Diana L. Thatcher, Alyssa C. Borowske, Victor J. Polyak, Alan D. Wanamaker, Rhawn F. Denniston, Caroline C. Ummenhofer, Nuno Bicho, Amanda N. Houts, Sebastian F. M. Breitenbach, Francisco Regala, and Michael M. Benedetti
- Subjects
geography ,Oceanography ,geography.geographical_feature_category ,Paleoceanography ,Stalagmite ,Glacial period ,Test (biology) ,Continental climate ,Geology - Published
- 2018
50. USING BULK AND COMPOUND SPECIFIC STABLE ISOTOPES IN ARCTICA ISLANDICA SHELLS TO RECONSTRUCT WESTERN NORTH ATLANTIC OCEAN DYNAMICS
- Author
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Alan D. Wanamaker, Katharine Luzier, Nina M. Whitney, Douglas S. Introne, Beverly J. Johnson, Erin Lower, Philip T. Dostie, Karl J. Kreutz, and Shelly M. Griffin
- Subjects
Ocean dynamics ,Oceanography ,biology ,Stable isotope ratio ,Compound specific ,biology.organism_classification ,Arctica islandica ,Geology - Published
- 2018
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