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Gram-negative bacterial 3-hydroxy fatty acids (3-OH-FAs) have received recent attention for their potential as palaeoclimate proxies. A novel temperature proxy, the ratio of anteiso to normal C13 3-OH-FA (RAN13), has been proposed for sea surface temperature (SST) reconstruction in the North Pacific Ocean. However, whether this newly proposed temperature proxy is applicable to marginal seas with significant terrigenous input or tropical oligotrophic seas requires further investigation. Here, we analyzed the composition and distribution of 3-OH-FAs and evaluated the possible impact of various environmental parameters (SST, water depth, dissolved oxygen, salinity and nutrient concentration) on their distribution in marine surface sediments from the Bohai Sea (BS) and the South China Sea (SCS). In the BS, the potential source proxy, fractional abundance of anteiso 3-OH-FAs (average 17%), indicates 3-OH-FA geochemical signature are not greatly overprinted by terrigenous inputs. The relative abundance of long-chain 3-OH-FAs (C15-C18) are higher in the SCS (average 41%) compared to those in other seas (average 33% for all marine samples). Massive inputs of terrigenous organic matter to the BS likely result in overestimation of SSTs based on the RAN13 proxy, and limited abundance of anteiso and normal C13 3-OH-FAs in the oligotrophic SCS may increase the uncertainty of the RAN13 estimated SSTs. More importantly, we find that most short-chain 3-OH-FAs are temperature dependent, especially the fractional abundance of i-C12, a-C13, i-C14 and n-C14 with a high determination coefficient (R2 > 0.60). Based on these newly found correlations, we propose a novel proxy: RANs. The RANs index shows a strong linear relationship with SST (R2 = 0.92, p< 0.001, n = 85) and more accurate prediction than the RAN13, especially in tropical samples. Furthermore, the RANs proxy is significantly correlated with TEX86, and RANs-based SSTs are approximate to LDI derived temperature in the SCS, which support the reliability of RANs as a temperature proxy. These findings further suggest 3-OH-FA based proxies have potential for paleo-SST reconstruction, especially at higher and lower ends of the ocean temperature spectrum and even in cases where marginal inputs of terrestrial organic matter and nutrients are high.

Understanding an animal's metabolic rate and thermal history is pivotal for ecological research. Recent studies have proposed the use of stable carbon and oxygen isotopes (δ13C and δ18O) in biogenic carbonates as proxies of metabolic rate and experienced temperature, respectively, to overcome the challenges of directly measuring these data in the field. Our study represents the first experimental investigation to develop δ13C and δ18O proxies in octopus. Octopus berrima hatchlings were raised in captivity, at varying water temperatures, for up to 110 days. O. berrima statoliths were then subsequently analysed for δ13C and δ18O values. The proportion of metabolically derived carbon, or respired carbon (C resp), increased as the octopus grew (slope = 0.076, R2 = 0.72), suggesting an influence of somatic growth rate and body mass on δ13C values. Additionally, we identified an inverse correlation between δ18O values and environmental temperature (slope = −0.163, R2 = 0.91), which was subsequently used to develop a thermal reconstruction model. Our experiment aids in interpreting stable isotopic values in statoliths and their application as temperature and metabolic proxies in wild-caught octopus. Such proxies will increase our monitoring capabilities of these ecologically and commercially significant cephalopods and contribute to their conservation and effective management. • Carbon isotopes have the potential to be proxies of metabolic rate in octopus. • Oxygen isotopes are effective at recording experience temperatures. • Our oxygen-temperature equation can calculate temperature for wild octopus. • Octopus incorporate carbon differently than fish. [ABSTRACT FROM AUTHOR]

Bivalve shells serve as powerful high-resolution paleoclimate archives. However, the number of reliable temperature proxies is limited. It has remained particularly difficult to extract temperature signals from shell Sr/Ca, although Sr is routinely employed in other biogenic aragonites. In bivalves, Sr/Ca is linked to the prevailing microstructure and is sometimes affected by kinetics. Here, the hypothesis is tested that temperature can be reconstructed from shell Sr/Ca once microstructure and/or growth-rate-related bias has been mathematically eliminated. Therefore, the relationship between Sr/Ca and increment width, as well as biomineral unit size, has been studied in three different shell portions of field-grown Arctica islandica specimens. Subsequently, microstructure and/or growth-rate-related variation was removed from Sr/Ca data and residuals compared to temperature. As demonstrated, the hypothesis could not be verified. Even after detrending, Sr/Ca remained positively correlated to water temperature, which contradicts thermodynamic expectations and findings from inorganic aragonite. Any temperature signal potentially recorded by shell Sr/Ca is overprinted by other environmental forcings. Unless these variables are identified, it will remain impossible to infer temperature from Sr/Ca. Given the coupling with the biomineral unit size, a detailed characterization of the microstructure should remain an integral part of subsequent attempts to reconstruct temperature from Sr/Ca. [ABSTRACT FROM AUTHOR]

The alkenones C37:2 and C37:3 are produced exclusively by some haptophyte species. Their relative proportion (Uk’37 index) may be used to infer the water temperature where the synthesising haptophyte lived. Alkenones have been analysed in sediments, planktonic communities and in the low trophic level, filter-feeding fin whales. However, it is unclear whether they can be detected in animals exploiting high trophic levels and used to infer the water temperature in which they live. Alkenones were analysed in blubber samples from three Mediterranean predatory species: the striped dolphin, an epipelagic species; the Risso’s dolphin, a deep diver; and the bottlenose dolphin, a coastal species. Alkenones were detected in all striped dolphin samples and in most of the Risso’s dolphin samples, but they were below detection limits in the bottlenose dolphin samples. The inferred temperature for the striped dolphins (16.4 ± 3.3 °C) was similar to the average water temperature of the region (16.9 ± 3.9 °C), but that for the Risso’s dolphins was lower than expected (12.7 ± 4.4 °C). The small sample sizes and the large variance in the Uk’37 index make it difficult to ascertain if the dissimilarity between the two oceanic species is real. Although further research is needed to calibrate this bio-indicator, we can conclude that alkenones are transferred through the trophic web and are found in oceanic cetaceans situated at a high trophic level.

Bivalve shells serve as powerful high-resolution paleoclimate archives. However, the number of reliable temperature proxies is limited. It has remained particularly difficult to extract temperature signals from shell Sr/Ca, although Sr is routinely employed in other biogenic aragonites. In bivalves, Sr/Ca is linked to the prevailing microstructure and is sometimes affected by kinetics. Here, the hypothesis is tested that temperature can be reconstructed from shell Sr/Ca once microstructure and/or growth-rate-related bias has been mathematically eliminated. Therefore, the relationship between Sr/Ca and increment width, as well as biomineral unit size, has been studied in three different shell portions of field-grown Arctica islandica specimens. Subsequently, microstructure and/or growth-rate-related variation was removed from Sr/Ca data and residuals compared to temperature. As demonstrated, the hypothesis could not be verified. Even after detrending, Sr/Ca remained positively correlated to water temperature, which contradicts thermodynamic expectations and findings from inorganic aragonite. Any temperature signal potentially recorded by shell Sr/Ca is overprinted by other environmental forcings. Unless these variables are identified, it will remain impossible to infer temperature from Sr/Ca. Given the coupling with the biomineral unit size, a detailed characterization of the microstructure should remain an integral part of subsequent attempts to reconstruct temperature from Sr/Ca.

Abstract Two small annually laminated stalagmites from Zoolithencave (southeastern Germany) grew between CE 1821 and 1970 (Zoo‐rez‐1) and CE 1835 and 1970 (Zoo‐rez‐2), respectively. Trace element concentrations were determined by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA‐ICP‐MS). Samples for δ13C and δ18O analyses were micromilled on annual and subannual resolution. Soil and host rock samples were analyzed by X‐Ray Diffraction (XRD) and their elemental concentrations determined via inductively coupled plasma optical emission spectrometer (ICP‐OES). Trace element concentrations in the stalagmites show two groups in the principal component analyses: one with Mg, Ba, and Sr and another with Y, P, and Al, respectively. The second group reflects the content of detrital material. Increased weathering of soil minerals seems to have a strong influence on the silicate/carbonate weathering ratio controlling the variability of Mg, Ba, and Sr. Meteorological and Global Network of Isotopes in Precipitation (GNIP) station data were used to calculate the δ18O values of the drip water (infiltration‐weighted, mean annual, and the mean of the winter precipitation δ18O values) as well as the corresponding speleothem calcite. The δ18O values calculated by the infiltration‐weighted model show similar patterns and amplitudes as the measured δ18O values of the two stalagmites. This suggests that the δ18O values of speleothem calcite reflect the δ18O values of infiltration‐weighted annual precipitation, which zis related to mean annual temperature, resulting in a significant correlation between mean annual temperature and the measured δ18O values of stalagmite Zoo‐rez‐2. This relationship could potentially be used for quantitative climate reconstruction in the future by extending the time series back in time with further stalagmites from Zoolithencave.

Two small annually laminated stalagmites from Zoolithencave (southeastern Germany) grew between CE 1821 and 1970 (Zoo‐rez‐1) and CE 1835 and 1970 (Zoo‐rez‐2), respectively. Trace element concentrations were determined by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA‐ICP‐MS). Samples for δ13C and δ18O analyses were micromilled on annual and subannual resolution. Soil and host rock samples were analyzed by X‐Ray Diffraction (XRD) and their elemental concentrations determined via inductively coupled plasma optical emission spectrometer (ICP‐OES). Trace element concentrations in the stalagmites show two groups in the principal component analyses: one with Mg, Ba, and Sr and another with Y, P, and Al, respectively. The second group reflects the content of detrital material. Increased weathering of soil minerals seems to have a strong influence on the silicate/carbonate weathering ratio controlling the variability of Mg, Ba, and Sr. Meteorological and Global Network of Isotopes in Precipitation (GNIP) station data were used to calculate the δ18O values of the drip water (infiltration‐weighted, mean annual, and the mean of the winter precipitation δ18O values) as well as the corresponding speleothem calcite. The δ18O values calculated by the infiltration‐weighted model show similar patterns and amplitudes as the measured δ18O values of the two stalagmites. This suggests that the δ18O values of speleothem calcite reflect the δ18O values of infiltration‐weighted annual precipitation, which zis related to mean annual temperature, resulting in a significant correlation between mean annual temperature and the measured δ18O values of stalagmite Zoo‐rez‐2. This relationship could potentially be used for quantitative climate reconstruction in the future by extending the time series back in time with further stalagmites from Zoolithencave. Key Points: Silicate versus carbonate weathering has an influence on speleothem trace elementsYttrium, phosphorus, and aluminum reflect detrital content of the speleothemsδ18O values of the stalagmites are a proxy for mean annual temperature [ABSTRACT FROM AUTHOR]

It is generally accepted that ice cores archive amount-weighted water stable isotope signals. In order to achieve an improved understanding of the nature of water stable isotope signals stored in ice cores annual δ18O and δ2H averages (i.e. amount-weighted) were calculated for two Antarctic meteorological stations, Vernadsky and Hal­ley Bay, using monthly precipitation amount and monthly net accumulation as weights, respectively. These were then compared with the annual mean δ18O δ2H and records of the nearest available ice cores. In addition, at the stations, both arithmetic means (i.e. time-weighted) and amount-weighted (precipitation amount and net accumulation used as weights) annual air temperature averages were calculated and then compared to amount weighted annual mean δ18O and δ2H using correlation- and regression analyses. The main hypothesis was that amount weighted annual mean water isotope and temperature records from the stations would be able to replicate the annual water isotope signal stored in ice cores to a higher degree. Results showed that (i) amount weighting is incapable of ameliorating the signal replication between the stations and the ice cores, while arithmetic means gave the stronger linear relationships; (ii) post depositional processes may have a more determining effect on the isotopic composition of the firn than expected; and (iii) mean annual air temperature provided the closest match to ice core derived annual water isotope records. This latter conveys a similar message to that of recent findings, in as much as ambient temperature, via equilibrium isotope fractionation, is imprinted into the uppermost snow layer by vapor exchange even between precipitation events. Together, these observations imply that ice core stable water isotope records can be a more continuous archive of near-surface temperature changes than hitherto believed.

The high-Mg calcite skeleton of Corallium rubrum was analyzed from living colonies collected from a wide range of depths (15 m to 607 m) and environmental settings in the Mediterranean Sea. An overarching goal was to better understand the calcification process and incorporation of elements into the slow-growing skeleton of both shallow and deep-water specimens, and more specifically, to clarify the veracity of geochemical proxies for reconstructing seawater temperatures. The coral internal structure including growth bands were determined by scanning electronic microscopy (SEM) and petrographic techniques. Trace elements (Li, B, Mg, Sr and Ba) compositions of the coral skeleton were obtained by solution and laser ablation inductively coupled plasma mass spectrometry (ICP-MS). Results show that the skeleton of the deep-water specimens has an internal microstructure similar to shallow-water colonies, with the medullar and the annular zones clearly distinguishable in both shallow and deep-water specimens. In general, the bands of the deep-water samples are very thin and equidistant compared to the irregular banding of the shallow-water specimens. Banding differences relate to the contrasting environmental dynamics, with the shallow-water specimens being exposed to large seasonal fluctuations compared to the relative stable conditions of those inhabiting bathyal depths. The inner medullar and outer annular portions differ in their trace element concentrations: Mg/Ca, Sr/Ca and Li/Ca ratios are higher in the medullar zone and seem to be influenced by growth kinetics, whereas B/Ca and Ba/Ca are similar in both zones and hence unaffected by growth rate. The variability of elemental ratios is lower in the deep-water specimens. Growth bands are highly correlated to Mg/Ca, Sr/Ca and Li/Ca, suggesting common mechanism(s) controlling the incorporation of these elements into the coral skeleton. Mg/Ca ratios were especially depleted in the dark bands. Although the mean Mg/Ca of each specimen is positively correlated to ambient seawater temperature, the intra-annual variations and amplitudes differ and do not correlate to the band widths. These findings suggest that intra- and inter-annual variations of Mg/Ca cannot be used to reconstruct a continuous time-series of long-term seasonal temperature records. However, the mean Mg/Ca composition can serve as a valuable proxy to estimate mean palaeoseawater temperature at a given site within the Mediterranean. • Shallow and deep-water Corallium rubrum have equivalent skeletal architecture, suggesting depth-independent growth patterns. • Mean Mg/Ca reconstructs mean temperature, while inter-annual timeseries reconstruction are hampered by vital effects. • Mg/Ca, Sr/Ca and Li/Ca from the annular zone are correlated, suggesting a common mechanism(s) of incorporation. • Mg/Ca, Sr/Ca and Li/Ca from the annular zone are correlated to radial width, while Ba and B are independent of growth rate. • Ba/Ca possibly reflects [Ba] sw with low concentrations in shallow-water and high concentrations at bathyal depth. [ABSTRACT FROM AUTHOR]

Abstract Mg/Ca ratios and oxygen isotope ratios (δ18O) in biogenic high‑magnesium calcite tests precipitated by reef-dwelling large benthic foraminifers can be used as paleotemperature proxies because they correlated well with the temperature of seawater. However, it is still unclear whether there is an interspecies difference in temperature correlation among several perforate and imperforate species. We used four species of large benthic foraminifer s to perform culture experiments at controlled temperatures (21–31 °C). Neorotalia calcar , Baculogypsina sphaerulata , and Calcarina gaudichaudii were selected as the perforate species, whereas Amphisorus kudakajimensis was chosen as the imperforate species. The data obtained by analyses suggest linear relations between Mg/Ca and temperature except at 31 °C, and also in the case of A. kudakajimensis except at 29 °C, which is likely caused by thermal stress resulting in metabolic anomaly in the foraminifers. Furthermore, A. kudakajimensis (imperforate species) had a different Mg/Ca–temperature equation form those of perforate species. The combined Mg/Ca–temperature and δ18O–temperature equations are yielded using the least square method as follows: Mg/Ca = 2.73 T + 74.7 for three perforate species, which is applicable to a temperature range between 21 °C to 30 °C. The temperature relation of δ18O is different even among perforate species. We observed that the δ18O values were closer to the equilibrium of pure calcite than those of high‑magnesium calcite. The δ18O–temperature (T) equations are yielded using the least square method as follows: T = 15.1–6.17 (δ18O c − δ18O sw) for C. gaudichaudii , T = 17.7–5.14 (δ18O c − δ18O sw) for N. calcar , and T = 16.1–5.10 (δ18O c – δ18O sw) for B. sphaerulata. A species-specific calibration is necessary for the relation between δ18O and temperature. As long as the optimum temperature range is the same, foraminifers belonging to the Calcarinidae show the same Mg/Ca–temperature relationship. Highlights • Four species of benthic foraminifers were cultured to evaluate the interspecies differences as a proxy for temperature. • Mg/Ca ratio in three species cultured at 31 °C deviated from linear temperature correlation. • The respective calibration was unnecessary for Mg/Ca–temperature relations for perforate species with the similar Mg/Ca range in the optimum. • The δ18O−temperature correlations needed species-specific calibrations among perforate species. [ABSTRACT FROM AUTHOR]

Alkenones are C 35 –C 42 polyunsaturated ketone lipids that are commonly employed to reconstruct changes in sea surface temperature. However, their use in coastal seas and saline lakes can be hindered by species-mixing effects. We recently hypothesized that freshwater lakes are immune to species-mixing effects because they appear to exclusively host Group I haptophyte algae, which produce a distinct distribution of alkenones with a relatively consistent response of alkenone unsaturation to temperature. To evaluate this hypothesis and explore the geographic extent of Group I haptophytes, we analyzed alkenones in sediment and suspended particulate matter samples from lakes distributed throughout the mid- and high latitudes of the Northern Hemisphere ( n = 30 ). Our results indicate that Group I-type alkenone distributions are widespread in freshwater lakes from a range of different climates (mean annual air temperature range: −17.3–10.9 °C; mean annual precipitation range: 125–1657 mm yr −1 ; latitude range: 40–81°N), and are commonly found in neutral to basic lakes (pH > 7.0), including volcanic lakes and lakes with mafic bedrock. We show that these freshwater lakes do not feature alkenone distributions characteristic of Group II lacustrine haptophytes, providing support for the hypothesis that freshwater lakes are immune to species-mixing effects. In lakes that underwent temporal shifts in salinity, we observed mixed Group I/II alkenone distributions and the alkenone contributions from each group could be quantified with the RIK 37 index. Additionally, we observed significant correlations of alkenone unsaturation ( U 37 K ) with seasonal and mean annual air temperature with this expanded freshwater lakes dataset, with the strongest correlation occurring during the spring transitional season ( U 37 K = 0.029 ⁎ T − 0.49 ; r 2 = 0.60 ; p < 0.0001 ). We present new sediment trap data from two lakes in northern Alaska (Toolik Lake, 68.632°N, 149.602°W; Lake E5, 68.643°N, 149.458°W) that demonstrate the highest sedimentary fluxes of alkenones in the spring transitional season, concurrent with the period of lake ice melt and isothermal mixing. Together, these data provide a framework for evaluating lacustrine alkenone distributions and utilizing alkenone unsaturation as a lake temperature proxy. [ABSTRACT FROM AUTHOR]

We evaluate the potential of calcareous dinoflagellates as archives for Sr/Ca-based paleo-temperature reconstructions and δ 44/40 Ca seawater fluctuations on sediments from Ocean Drilling Program Expedition 113 (Hole 690C, Weddell Sea, Southern Ocean). Between 73 and 68 Ma, Sr/Ca ratios of two Cretaceous dinoflagellate species, Pirumella krasheninnikovii and Orthopithonella globosa show a pronounced decrease, consistent with a significant drop in sea-surface temperature as reflected by the δ 18 O of planktic foraminifers. The apparent temperature sensitivity of the dinoflagellate cysts' Sr/Ca is ~0.06 and ~0.08 mmol/mol °C −1 , using δ 18 O-derived paleo sea-surface temperatures, which is significant and large enough to resolve paleoenvironmental temperature changes at current analytical precision. As the chemical composition of the cyst calcite appears to have a good preservation, the Sr/Ca of calcareous dinoflagellates has a potential to serve as paleo-temperature proxy, although the chemical composition of the Cretaceous seawater and potential impacts on the cyst geochemistry is pending further inspection. The Ca isotope composition of the two dinoflagellate species shows identical trends of increasing δ 44/40 Ca between 73 and 67 Ma. The planktic foraminifer Archaeoglobigerina australis and the benthic foraminifer Nuttallides truempyi reveal the same increase of about 0.4‰ but are offset relative to the dinoflagellates by about +0.5‰, presumably due to species-specific Ca isotope fractionation. Bulk carbonate sediment shows significant scatter, likely caused by changes in faunal composition and does not reproduce the trend revealed by the dinoflagellate and foraminifer records. These observations demonstrate the importance of taxon-specific records and careful determination of fractionation factors of selected archives and highlight complications arising from utilizing less suitable archives, such as bulk sediments, for δ 44/40 Ca seawater reconstructions. Our records indicate strong changes in the marine Ca cycle associated with the global temperature decrease towards the end of the Cretaceous. [ABSTRACT FROM AUTHOR]

The oxygen isotope composition (δ 18 O) recorded in shells of the gastropods Patella candei crenata and Phorcus atratus from the Canary Islands (27–29°N) potentially provide invaluable high-resolution paleoclimatic data. However, because these two species have never been studied isotopically, it is necessary to calibrate and validate this approach by using live-collected specimens that can be compared to present-day climate data. For P. candei crenata , live organisms were collected at 15-day intervals for nearly one year (between 2011 and 2012) from the rocky-intertidal coast of SE Tenerife along with sea surface temperatures (SST) and seawater δ 18 O values. The δ 18 O values of the last growth episode along the shell growth margin, representing the conditions when organisms were collected, illustrate that P. candei crenata δ 18 O values were 1.3 ± 0.2‰ higher than expected values from isotopic equilibrium. This finding resulted in estimated SST 5.7 ± 0.6 °C lower than observed values. This offset or “vital effect” is uniform and predictable, and therefore can be corrected by subtracting 1.3‰ from the measured shell δ 18 O value. Adjusted temperatures from the shell coincided with observed SST in the study area. Therefore, Patella candei crenata shells are reliable repositories of SST data, in agreement with other species of Patella from higher latitudes. For Phorcus atratus , a live specimen was analyzed isotopically along shell-growth direction. The intrashell δ 18 O values showed the entire range of measured SST in the region without an apparent “vital effect”, in correspondence with other Phorcus species from the Mediterranean. Both Patella candei crenata and Phorcus atratus are common components of archaeological and Pleistocene-Holocene paleontological sites across the Canary Archipelago. This study suggests that well-preserved shells of these two taxa retrieved from ancient settings have the capacity to serve as excellent high-resolution paleotemperature archives for the tropical/subtropical eastern Atlantic region. [ABSTRACT FROM AUTHOR]

Rapid climate warming has resulted in shrub expansion, mainly of erect deciduous shrubs in the Low Arctic, but the more extreme, sparsely vegetated, cold and dry High Arctic is generally considered to remain resistant to such shrub expansion in the next decades. Dwarf shrub dendrochronology may reveal climatological causes of past changes in growth, but is hindered at many High Arctic sites by short and fragmented instrumental climate records. Moreover, only few High Arctic shrub chronologies cover the recent decade of substantial warming. This study investigated the climatic causes of growth variability of the evergreen dwarf shrub Cassiope tetragona between 1927 and 2012 in the northernmost polar desert at 83°N in North Greenland. We analysed climate-growth relationships over the period with available instrumental data (1950-2012) between a 102-year-long C. tetragona shoot length chronology and instrumental climate records from the three nearest meteorological stations, gridded climate data, and North Atlantic Oscillation ( NAO) and Arctic Oscillation ( AO) indices. July extreme maximum temperatures (JulTemx), as measured at Alert, Canada, June NAO, and previous October AO, together explained 41% of the observed variance in annual C. tetragona growth and likely represent in situ summer temperatures. JulTemx explained 27% and was reconstructed back to 1927. The reconstruction showed relatively high growing season temperatures in the early to mid-twentieth century, as well as warming in recent decades. The rapid growth increase in C. tetragona shrubs in response to recent High Arctic summer warming shows that recent and future warming might promote an expansion of this evergreen dwarf shrub, mainly through densification of existing shrub patches, at High Arctic sites with sufficient winter snow cover and ample water supply during summer from melting snow and ice as well as thawing permafrost, contrasting earlier notions of limited shrub growth sensitivity to summer warming in the High Arctic. [ABSTRACT FROM AUTHOR]

Coral skeletons preserve useful archival indicators from which to reconstruct past environments. We conducted temperature-controlled culture experiments (20, 22, 27, and 31 °C) with primary polyps of Acropora digitifera to accurately assess the impact of a wide range of temperatures on the calcification rate and to methodically evaluate the skeletal trace elements (Sr/Ca, Mg/Ca, and Na/Ca ratios). Water temperatures positively affected the calcification rate up to 31 °C, which exceeds the temperature threshold for this species. The calcification rates also varied widely (> 20%) during each of the four temperature treatments. The skeletal Sr/Ca ratio was most strongly correlated with water temperature ( R 2 = 0.68, p < 0.001), whereas the Mg/Ca and Na/Ca ratios showed lower correlations ( R 2 = 0.53, p < 0.001; R 2 = 0.34, p = 0.011, respectively). The variations in the skeletal Sr/Ca, Mg/Ca, and Na/Ca ratios at the four different temperatures were 0.36%–1.20%, 0.83%–3.76%, and 0.52%–3.24%, respectively. Thus, the Sr/Ca ratio showed the least variation, despite the wide variations in the calcification rate. We confirm that the Sr/Ca ratio of A. digitifera juveniles is a robust proxy of temperature, regardless of variations in the calcification rate and the wide range of ambient temperatures. In addition, our results regarding skeletal Mg/Ca and Na/Ca ratios further our understanding of coral calcification processes. [ABSTRACT FROM AUTHOR]

We evaluated the use of the stable oxygen isotope (δ 18 O) in the otolith as a proxy for the temperature history of Japanese sardine Sardinops melanostictus individuals. Japanese sardine juveniles were reared in three different water temperatures over the course of a month. Otolith δ 18 O ( δ otolith ) was analyzed by extracting the portions formed during the rearing period using a micromill. δ 18 O of the rearing water ( δ water ) was also analyzed. A linear relationship between otolith δ 18 O and ambient water temperature was identified as follows: δ otolith − δ water = −0.18 * T + 2.69 (r 2 = 0.91, p < 0.01). This equation is different from that proposed for inorganic aragonite or other Sardinops spp., with resulting application to wild Japanese sardine captured in the Pacific Ocean showing that it estimates a more realistic in situ temperature. Our findings suggest that the Japanese sardine-specific isotopic fractionation equation should be used when interpreting otolith δ 18 O of the Japanese sardine, and the methods presented here could also be useful to understand the temperature history of other fish species. [ABSTRACT FROM AUTHOR]

This paper presents chironomid-based transfer functions for temperature reconstructions intended for use in the Australian tropics and sub-tropics. Temperature was the primary independent control of chironomid assemblages. Two transfer functions were created to infer mean annual (MAT) and mean summer temperature as represented by February temperatures (MFT) as it was not reasonable to automatically assume that chironomid populations in the tropics are controlled by summer temperatures. Weighted average partial least square (WA-PLS) models were the most robust. For MAT they produced a coefficient of determination (r 2 jack ) of 0.83, a maximum bias of 1.74 °C and a root mean squared error of prediction (RMSEP) of 2.35 °C while for MFT an r 2 jack of 0.76, maximum bias of 2.43 °C, and RMSEP of 2.43 °C was achieved. Based on the statistics we recommend that the MAT model is used for chironomid work in tropical regions. Though chironomid head capsule counts were low, we tentatively applied the MAT function to published Holocene chironomid data from Lake Barrine, northeast Queensland. The results suggest only minor temperature change through the last 9000 years. Based on other proxies, this appears to result in realistic temperature reconstructions. Consequently we highlight that sub-fossil chironomids have the potential to provide high quality temperature records for the Australian tropics. [ABSTRACT FROM AUTHOR]

Shells of bivalves potentially provide an excellent archive for high-resolution paleoclimate studies. However, quantification of environmental variables, specifically water temperature remains a very challenging task. Here, we explore the possibility to infer water temperature from changes of microstructural characteristics of shells of the common cockle, Cerastoderma edule . The size and elongation of individual microstructural units, i.e., prisms, in the outer shell layer of seven three to five year-old, specimens collected alive from the intertidal zone of the North Sea near Texel, The Netherlands, and Schillig, Germany, were measured by means of automatic image processing. Growth patterns (circatidal, ciralunidian and fortnightly increments and lines), shell oxygen isotope values and mark-and-recovery experiments were used to place the shell record in a precise temporal context. Irrespective of the locality and ontogenetic age, size and elongation of the prisms increased non-linearly with water temperature. Small (0.12 ± 0.05 μm 2 ) and round prisms (elongation: 2.42 ± 0.31) were formed at temperatures of ca. 10 °C (late April), whereas larger (0.33 ± 0.11 μm 2 ) and more elongated prisms (3.26 ± 0.28) occurred during hot summer (ca. 22 °C). No clear-cut or consistent correlation existed between microstructural characteristics and growth rate as well as a variety of other environmental variables such as salinity, chlorophyll a and turbidity. Based on these findings, a model was constructed from three shells at Texel that enables reconstruction of water temperature with a precision of 1.7 ± 1.0 °C from prism size and elongation: SST = 9.02 + 17.25 P s + 1.10 P e . This model was successfully tested at four shells from Schillig. The new temperature proxy can be of particular interest for paleoclimate studies in nearshore settings when non-recrystallized C. edule shells are available. Future studies are required to verify our findings and check if other species with the same and different microstructures show similar relationships with water temperature. [ABSTRACT FROM AUTHOR]

Estimating chronological uncertainty is a critical but often neglected prerequisite in palaeoclimatological reconstructions and core comparisons. We describe a hierarchical Bayesian multinomial regression model for temperature reconstruction that allows uncertainty in the sediment core sample dates. Climate model output is used as pseudodata to provide prior information about the overall variability of past temperatures. Including time uncertainty in the model can make usual summaries such as the posterior mean temperature less useful. We therefore recommend considering also fixed chronology reconstructions and exploration of individual temperature history realizations. This can be particularly relevant for tracking short-lived events. We demonstrate the proposed model by reconstructing the past temperature from fossil pollen data obtained from three cores in Estonia and southern Sweden. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Coccoliths have dominated the sedimentary archive in the pelagic environment since the Jurassic. The biominerals produced by the coccolithophores are ideally placed to infer sea surface temperatures from their oxygen isotopic composition, as calcification in this photosynthetic algal group only occurs in the sunlit surface waters. In the present study, we dissect the isotopic mechanisms contributing to the “vital effect”, which overprints the oceanic temperatures recorded in coccolith calcite. Applying the passive diffusion model of carbon acquisition by the marine phytoplankton widely used in biogeochemical and palaeoceanographic studies, our results suggest that the oxygen isotope offsets from inorganic calcite in fast dividing species Emiliania huxleyi and Gephyrocapsa oceanica originates from the legacy of assimilated 18 O-rich CO 2 that induces transient isotopic disequilibrium to the internal dissolved inorganic carbon (DIC) pool. The extent to which this intracellular isotopic disequilibrium is recorded in coccolith calcite (1.5 to +3‰ over a 10 to 25 °C temperature range) is set by the degree of isotopic re-equilibration between CO 2 and water molecules before intracellular mineralisation. We show that the extent of re-equilibration is, in turn, set by temperature through both physiological (dynamics of the utilisation of the DIC pool) and thermodynamic (completeness of the re-equilibration of the relative 18 O-rich CO 2 influx) processes. At the highest temperature, less ambient aqueous CO 2 is present for algal growth, and the consequence of carbon limitation is exacerbation of the oxygen isotope vital effect, obliterating the temperature signal. This culture dataset further demonstrates that the vital effect is variable for a given species/morphotype, and depends on the intricate relationship between the environment and the physiology of biomineralising algae. [ABSTRACT FROM AUTHOR]

The clumped isotope geothermometer estimates the formation temperature ( T ( Δ 47 ) ) of carbonates and has great potential to enhance the extraction of environmental data from pedogenic (soil) carbonate in the geologic record. However, the influence of vegetation type and site-specific conditions on carbonate formation processes and T ( Δ 47 ) records remains poorly understood. This study examines the potential for variability in T ( Δ 47 ) data between nearby, same elevation sites with different C 3 /C 4 biomass. Pedogenic carbonates (undercoatings and nodules) were collected from five modern soil pits in the semi-arid eastern Andean piedmont of Argentina under a summer precipitation regime. Three pits were instrumented with temperature and moisture sensors to 1 m depth, and a fourth was instrumented with additional soil CO 2 and atmospheric (temperature, relative humidity, insolation, and rainfall) sensors. T ( Δ 47 ) values (mean: 30 ± 6 ° C (±1SE)) are invariant with depth and are statistically indistinguishable between the four instrumented sites, though a 10 °C difference between our T ( Δ 47 ) values and those of a nearby Peters et al. (2013, EPSL) study suggests the potential for significant site-to-site variability, likely due to local soil hydrology. The results of this study suggest that deeper (≥40 cm) T ( Δ 47 ) values are consistent with carbonate formation during the early part of soil drying immediately after large mid-summer rainstorms. Carbonate formation ≤ 40 cm depth may be biased to soil drying after small, frequent precipitation events occurring throughout the spring, summer, and fall months, averaging to shallow summer T ( Δ 47 ) values and resulting in a near-isothermal T ( Δ 47 ) profile. [ABSTRACT FROM AUTHOR]

Quantitative reconstruction of water temperature from shells of bivalve mollusks is still a very challenging task. For example, in highly variable environments such as intertidal zones, shell oxygen isotope values can only provide reliable temperature estimates if the δ 18 O water signature during the time of growth is known. Furthermore, trace element-to-calcium ratios such as Sr/Ca or Mg/Ca often do not serve as reliable paleothermometers, because their incorporation into bivalve shells is known to be strongly biologically controlled. Here, we present a potential novel temperature proxy which is based on the Sr/Li shell ratio of the intertidal bivalve Cerastoderma edule . Up to 81% of the variability in Sr/Li shell is mathematically explained by water temperature. It is suggested that vital effects on the incorporation of Sr and Li into the aragonitic shells are largely eliminated by normalizing Sr/Ca to Li/Ca. Growth rate does not control the incorporation of Sr or Li into the shell of C. edule . By using this new proxy, it was possible to estimate water temperature from C. edule with an uncertainty of ± 1.5 °C. Future studies are required to test if Sr/Li shell also serves as a reliable temperature proxy in other bivalve species and in other environments. [ABSTRACT FROM AUTHOR]

Abstract: The ice-loaded Labrador Current (LC) is an important component of the western North Atlantic circulation that influences the position and strength of the northern limb of the North Atlantic Current (NAC). This flow of cold and fresh Polar Waters originating from the Arctic has a marked impact on the North Atlantic climate, yet little is known about its variability beyond the instrumental period. In this study, we present the first sub-decadal alkenone-based 2000-year long sea-surface temperature (SST) records from the western Labrador Sea, a climatically crucial region at the boundary between the LC and the NAC. Our results show a clear link between the LC strength and the Northern Annular Mode (NAM), with a stronger NAM and a more vigorous LC during the Medieval Climate Anomaly (MCA). This suggests enhanced LC activity upon future global warming with implications for the Atlantic meridional overturning circulation (AMOC). [Copyright &y& Elsevier]

Branched glycerol dialkyl glycerol tetraether (GDGT) distributions observed in a sediment core from Lake McKenzie were utilized to quantitatively reconstruct the pattern of mean annual air temperature (MAAT) from coastal subtropical eastern Australia between 37 and 18.3calkaBP and 14.0calkaBP to present. Both the reconstructed trend and amplitude of MAAT changes from the top of the sediment core were nearly identical to a local instrumental MAAT record from Fraser Island, providing confidence that in this sediment core branched GDGTs could be used to produce a quantitative record of past MAAT. The reconstructed trend of MAAT during 37 to 18.3calkaBP and timing of the Last Glacial Maximum (LGM) in the Lake McKenzie record were in agreement with previously published nearby marine climate records. The amplitude of lower-than-present MAAT during the LGM potentially provides information on the latitude of separation of the Tasman Front from the East Australian current in the subtropical western Pacific. The Lake McKenzie record shows an earlier onset of near modern day warm temperatures in the early Holocene compared to marine records and the presence of a warmer than present day period during the mid-Holocene. [ABSTRACT FROM AUTHOR]

Abstract: A year-long controlled growth experiment of 60 specimens of the Antarctic bivalve Adamussium colbecki was conducted in Terra Nova Bay (Ross Sea) to evaluate its reliability as a suitable archive of water mass properties. Nine shells were sub-sampled for stable oxygen and carbon isotope analysis to study the inter and intra specimen variations. Slow-growing A. colbecki precipitate their calcitic shells close to the expected oxygen and carbon isotopic equilibrium, whereas the fast-growing individuals are strongly influenced by biogenetic and kinetic effects. The equation of Kim and O'Neil (1997) is considered a fair approximation for the δ18O-temperature relationship in slow-growing individuals. The reconstructed temperature is closer to the mean experimental summer temperature than the annual one. This fact is interpreted as reflecting a possible winter decrease of shell growth, the salinity variation and the corrections for negative temperature on calibrating the δ18O-temperature relationship. Our results support the hypothesis that A. colbecki might represent a good archive for encoding Antarctic Shelf water summer temperature information. Further improvements in adopting A. colbecki as a paleotemperature archive will require the evaluation of the seasonal variability in shell growth rate through culturing slow-growing A. colbecki individuals at near-freezing temperatures to calibrate a species-specific δ18O-temperature equation. [Copyright &y& Elsevier]

Abstract: Quantifying the timing and temperature of soil carbonate formation is important for interpreting isotopic records of Earth-surface temperature and soil water composition from paleosols. Pedogenic carbonates typically have been assumed to form at mean annual temperature, but recent work suggests warm-season bias in carbonate formation could impact the interpretation of δ 18O values and carbonate formation temperatures for paleosol carbonates. We investigate the relationship between seasonally variable soil temperatures and carbonate formation temperatures estimated using clumped isotope thermometry (T(Δ47)). Holocene soil carbonates were collected along the eastern flank of the Andes (33°S) over 2km of relief and a nearly 15°C range of mean annual air temperature (MAAT). This area receives both westerly, winter season precipitation and easterly, summer season precipitation, leading to a reversal of soil moisture regimes that occurs at ∼2km elevation. In instrumented pits sampled to 1m depth, we do not observe systematic variation in T(Δ47) with depth or with elevation-dependent MAAT. Average T(Δ47) values for soil carbonates collected above 2km elevation reflect summer soil temperatures. In contrast, T(Δ47) values below ∼2km track mean annual soil temperature. These results may reflect the dominance of summer precipitation below ∼2km, which likely delays soil drying and carbonate growth until fall. This seasonal variability in carbonate formation greatly impacts carbonate formation temperature, with important implications for estimating soil water δ 18O values. Calculating soil water δ 18O values using T(Δ47) produces a soil water δ 18O lapse rate of −4.6‰/km, remarkably similar to that of modern surface waters (−4.8‰/km), and significantly improving on previous soil water estimates assuming MAAT for carbonate formation temperatures. Although seasonal bias can prevent the straightforward translation of soil carbonate T(Δ47) into meaningful surface air temperatures, direct constraints on temperature from clumped isotopes can both provide a window into soil processes and aid in the interpretation of conventional stable isotopic data to reconstruct surface conditions in the past. [Copyright &y& Elsevier]

The relationship between water temperature, growth rate, and otolith isotopic ratios was measured for juvenile plaice ( Pleuronectes platessa) reared at two temperatures (11 and 17°C) and two feeding regimes (1 and 3 prey items·ml). The otolith isotope ratios in individual fish ranged from −2 to −4 for carbon isotope ratios (δC) and from 0.2 to 1.9 for oxygen isotope ratios (δO). The otolith oxygen isotope ratios were significantly affected by water temperature, but not by feeding level, and there were no significant synergistic effects. The fractionation of oxygen isotopes during otolith growth was independent of individual growth rate. Carbon isotope ratios were not significantly affected by food ration or water temperature, but were related to fish growth rate. The carbon isotope ratios were negatively correlated with fish length in the colder water treatments, and tended to increase with fish length in the warm water treatments. The laboratory-determined relationship between otolith oxygen isotope ratio and water temperature was applied to individuals of five species (plaice, cod, whiting, haddock, gurnard) collected in a single trawl sample. The otolith derived temperatures often overestimated measured water temperatures. The difference between real and estimated water temperatures varied between species, and the closest fit was for field-caught plaice. [ABSTRACT FROM AUTHOR]

Acquiring continuous and high-resolution natural records in recent 2,000 years is the hot issue in the palaeoclimate research. Recent studies revealed that Li/Ca and Mg/Li ratio of carbonate is a potential tracer of past environmental changes in the oceans, and is seldom applied for palaeoclimate reconstruction in lakes. To make full understanding of the potential of Li/Ca ratios of carbonates in lakes, Li/Ca ratios of monospecific ostracod shell Eucypris inflate with similar size in the lacustrine sediment core from Lake Qinghai, NE Tibetan Plateau have been analysed for the first time. Single species can effectively avoid the interspecies effects. In combination with the sedimentation rate that existed, data derived from Pb and Cs, downcore variations of Li/Ca ratios of ostracod shells during the past 800 years in Lake Qinghai have been reconstructed successfully. By comparing Li/Ca ratios and temperature inferred from meteorological records and tree ring widths in Dulan and Qilianshan in adjacent regions, Li/Ca ratios of ostracod shells negatively correlate with temperature. Higher temperature corresponds with lower Li/Ca ratios, and vice versa, indicating that Li/Ca ratio of ostracod shells is an effective indicator for temperature variations. Therefore, ongoing in-depth investigation using Li/Ca ratios of carbonates in more lakes to further reveal its palaeotemperature implications would be deserved. [ABSTRACT FROM AUTHOR]

Abstract: Coccoliths from cultured specimens of two species of coccolithophores (Emiliania huxleyi and Gephyrocapsa oceanica) were sampled during two growth phases (late exponential and stationary), and their Mg isotope values (δ 26Mg) as well as Mg/Ca values were measured in order to investigate whether δ 26Mg can be used as a temperature proxy. Mg/Ca values were positively related with temperature (~0.002mmol/mol/°C), without statistically significant differences between the two growth phases and the two species. Both species were depleted in heavier Mg isotopes relative to the culture medium, and δ 26Mg values were temperature dependent in both growth phases of E. huxleyi, although the δ 26Mg values differed in the two growth phases. In G. oceanica, a weak correlation between δ 26Mg values and temperature was seen in the late exponential growth phase only, and the δ 26Mg values differed between growth phases. The large differences between δ 26Mg values as measured in calcite formed during different growth phases indicate that Mg isotopes of coccoliths cannot be simply used as a temperature proxy. Our conclusions are preliminary and more data must be collected in order to fully evaluate the use of Mg isotopes of coccoliths as a temperature proxy. [ABSTRACT FROM AUTHOR]

Height increments of 60 Scots pine trees were used to reconstruct mean June-August temperature variability at interannual to decadal scales from 1561 to 2004. Three standardization methods (67%, 33% flexible splines, and a fixed 22 years spline) were compared in building chronologies in order to optimize the frequency response in relation to major climatic forcing factors. The height-growth chronology built using the 33% spline standardization proved to have the most consistent and time-stable relationship with the summer temperatures. Among the monthly precipitation and temperature variables from previous June to current August, previous July shows the highest correlation with height growth. In addition, both previous June and previous August have significant positive correlations. Our final transfer model accounts for 32.5% of the dependent instrumental temperature variance between 1909 and 2004. The Fourier spectra of the height-growth chronology and mean summer temperature are very similar in appearance, both series having peaks at 2.7-3.2 years, 6.7 years and 15.7 years. Thus, the 444 years long summer temperature reconstruction is limited to high and medium frequencies. The coldest three summers in this record were experienced in years 1601, 1790 and 1903. Correspondingly, the summers of 1626, 1689 and 1598 were the warmest. The 1820s experienced the warmest 10-year mean, while the first decade of the twentieth century was the coldest. Among the 14 non-overlapping 30-year periods between 1561 and 1980, the period 1621-1650 was the warmest and the period 1591-1620 the coldest. [ABSTRACT FROM AUTHOR]

Abstract: Zooxanthellate scleractinian corals are known as archives for temporal variations of climate variables, such as sea surface temperature, salinity or productivity. The use of azooxanthellate cold-water corals as potential archives for intermediate water mass properties and climate variability was tested recently. However, the correlation of established proxies such as δ 18O and δ 13C with temperature is difficult since there is no direct temperature equation applicable as in shallow-water corals. Other temperature proxies such as Sr/Ca, Mg/Ca and U/Ca are influenced by the complex microstructure of the aragonite skeleton, the rate of calcification, and other vital effects observed for coral species. For the first time we show that the stable strontium isotope ratio δ 88/86Sr incorporated in the skeletons of the cold-water coral species Lophelia pertusa portrays the ambient seawater temperature. The temperature sensitivity from live samples collected along the European continental margin covering a temperature range from 6° to 10 °C is 0.026±0.003‰/°C (2σ standard error) which is a sensitivity similar to the tropical shallow-water coral record of Pavona clavata. This indicates a similar fractionation process of strontium for both, zooxanthellate and azooxanthellate corals. For coral aragonite the δ 88/86Sr ratio may serve as a new paleo-temperature proxy and introduces new perspectives in paleoceanography with respect to intermediate water dynamics. [Copyright &y& Elsevier]

Abstract: Studies using oxygen isotopes (δ18O) of mollusk shells to determine paleotemperature need to assume water δ18O values, which could severely influence calculated temperatures. We analyzed aragonitic shells of the Butter Clam, Saxidomus giganteus (DeShayes, 1839), to determine the reproducibility of the isotopic signal between individuals and to assess how precisely temperature could be calculated given known salinity and temperature. Furthermore, carbon isotopes are also investigated as an environmental proxy. The abundance of well-preserved S. giganteus shells in archeological and geological deposits in northwestern North America makes them a particularly suitable species for paleoclimate studies. Seasonally resolved stable oxygen isotope profiles in three S. giganteus shells collected from the same site in Puget Sound (Washington, USA) were well correlated (0.77< R 2 <0.87). Although there were differences up to 0.58‰ in high resolution δ18O profiles of the three shells, the difference between the average δ18O of each shell was less than half of this (0.19‰) and half of what has been reported for between-colony coral variability. δ13C profiles on the other hand were more complex, with shell δ13C being about 2.5‰ lower than expected equilibrium values. However, this roughly conforms to the idea that about 10% of the shell carbon originates from metabolic CO2. Both δ18O and δ13C indicate that S. giganteus do not grow during periods of reduced salinity. Despite the excellent reproducibility of δ18O between shells, and the fact that salinity effects were duly considered, calculated temperature still differed from instrumental temperature. Applying different salinity–δ18O water relationships to average shell δ18O, and considering salinity from the shell collection site and a nearby offshore station resulted in calculated average water temperatures ranging from 1.7 to 6.4 °C warmer than measured. Although we could not determine if S. giganteus precipitate their shells in isotopic equilibrium, we believe that the difficulty in predicting temperature arose from not being able to accurately determine δ18O of the water at the time of shell precipitation. These data highlight the difficulties inherent to using stable isotope profiles of estuarine biogenic carbonates as environmental proxies. [Copyright &y& Elsevier]

• Distinct distributions of 3-OH-FAs are found in soils, marine- and lake sediments. • First systematic investigation of 3-OH-FAs in lake environments. • We propose a novel temperature proxy based on 3-OH-FAs for lake environments. Bacterial 3-hydroxy fatty acids (3-OH-FAs) show potential for terrestrial paleoclimate reconstruction; however, the possibility of using 3-OH-FAs as proxies in lacustrine environments remains to be investigated. We analysed the composition and distribution of 3-OH-FAs in surface sediments from 20 Chinese alkaline lakes and investigated the development of climate proxies based on 3-OH-FAs in these lacustrine environments. The results show that lake sediments contain higher relative abundances of anteiso 3-OH-FAs compared to soils. Analysis of the gene community composition from Lake Liangzi reveals that Gram-negative bacterial communities in that lake environment are distinct from marine sediments from the South China Sea but share many characteristics with soils from Mt. Yujia at the phylum level. At the class level, the Lake Liangzi samples yield distinctly higher proportions of Deltaproteobacteria (23%), Betaproteobacteria (13%), Gammaproteobacteria (14%), and Bacterioidia (10%). pH proxies based on 3-OH-FAs (Branching Ratio, Branched index, RIN and RIAN) yield weak linear relationships with lake water pH, while RAN 13 (previously proposed as a sea surface temperature proxy) shows a linear relationship with mean annual air temperatures (MAAT; ranging from 5 °C to 17 °C). The soil temperature proxies RAN 15 (previously applied to a stalagmite) and RAN 17 do not appear to be suitable for temperature calibration in lacustrine environments. We propose a novel temperature proxy (RIN 17 , ratio of iso to normal C 17 3-OH-FA) for lake environments. These field-based correlations demonstrate that the physiological response of Gram-negative bacterial cell membranes to external environmental changes are recorded in lake sediments on a large regional scale. This further highlights the potential use of bacterial 3-OH-FAs as proxies for paleoclimate reconstruction in both aquatic and terrestrial environments. [ABSTRACT FROM AUTHOR]

• C37 alkenones are transferred through the pelagic trophic web. • Alkenones can be detected in pelagic top predators, but not in coastal ones. • The Uk' 37 appears consistent with the sea surface temperature in the epipelagic species. The alkenones C 37:2 and C 37:3 are produced exclusively by some haptophyte species. Their relative proportion (Uk' 37 index) may be used to infer the water temperature where the synthesising haptophyte lived. Alkenones have been analysed in sediments, planktonic communities and in the low trophic level, filter-feeding fin whales. However, it is unclear whether they can be detected in animals exploiting high trophic levels and used to infer the water temperature in which they live. Alkenones were analysed in blubber samples from three Mediterranean predatory species: the striped dolphin, an epipelagic species; the Risso's dolphin, a deep diver; and the bottlenose dolphin, a coastal species. Alkenones were detected in all striped dolphin samples and in most of the Risso's dolphin samples, but they were below detection limits in the bottlenose dolphin samples. The inferred temperature for the striped dolphins (16.4 ± 3.3 °C) was similar to the average water temperature of the region (16.9 ± 3.9 °C), but that for the Risso's dolphins was lower than expected (12.7 ± 4.4 °C). The small sample sizes and the large variance in the Uk' 37 index make it difficult to ascertain if the dissimilarity between the two oceanic species is real. Although further research is needed to calibrate this bio-indicator, we can conclude that alkenones are transferred through the trophic web and are found in oceanic cetaceans situated at a high trophic level. [ABSTRACT FROM AUTHOR]

The blue intensity (BI) technique provides opportunities to obtain surrogates to tree-ring density for reconstructing summer temperatures in high-latitude regions. In this study, we compare latewood BI (LBI) and delta BI (DBI), with the conventional X-ray maximum latewood density (MXD) and tree-ring width (TRW) data using 178 living trees of black spruce (Picea mariana (Mill.) B.S.P.), one of the most dominant species of conifers in the Northern Hemisphere, from 17 sites across the eastern Canadian taiga. The regional LBI and DBI chronologies are highly correlated to that of MXD (Pearson's r = 0.97 and 0.92, respectively), while DBI is also similar to TRW (Pearson's r = 0.67). Both LBI and DBI exhibit stronger responses to the May–August temperatures than TRW over larger time and spatial scales. However, only DBI is comparable to MXD data from inter-annual to decadal timescales. Low-frequency components of LBI data are likely distorted by color biases even if no obvious discoloration is present, as well as by the potentially low measurement resolution, leading to an overall weaker temperature sensitivity compared to the MXD data. Resampling experiments suggest that a minimum replication of 10 trees is needed to retain ≥90 % of the optimal temperature signal for MXD, LBI, and DBI data, and a minimum of 20 trees is required for TRW data. [ABSTRACT FROM AUTHOR]

Our recent study suggests that branched glycerol dialkyl glycerol tetraethers (brGDGTs) in ancient bones may have great potential for reconstructing in-situ paleoclimate conditions. However, one major problem with reconstructing past climate and environmental conditions using brGDGTs in ancient bones is the lack of calibrations specific to bones. Here we investigate the distribution of brGDGTs in 191 modern weathered bone samples in China with a broad range of mean annual air temperature (MAAT: −3.3-25.6 °C) and mean annual precipitation (MAP: 163-2062 mm), and present the first bone-specific brGDGT temperature and precipitation calibrations. We find that the best correlation with temperature is found in bones with a higher ratio of 6-methyl over 5-methyl brGDGT isomers, suggesting a preferential production of 6-methyl brGDGTs by bacteria inside bones. The bone-specific temperature relationship is distinct from published mineral soil calibrations (e.g., with virtually no influence from soil pH changes). We hypothesize that the lower calibration residual values result from more homogenous and semi-closed environment for bacterial growth inside the bones than soil environments. We also demonstrate that, in semi-arid and semi-humid regions (MAP: 200-710 mm), brGDGT distributions in cancellous bones with relatively high percentages of 6-methyl isomers are strongly correlated with mean annual precipitation. Application of our bone-specific brGDGT calibrations to Alaskan chronological sequences yields new insights to high latitude temperature and precipitation variations for the past 30,000 years. • First bone-specific brGDGT temperature and precipitation calibrations established. • Correlation with temperature increases in bones with high 6-methyl brGDGT isomers. • A new precipitation index is proposed for arid and semi-arid regions. • Relatively warm LGM in Alaska attributed to regional atmospheric circulation. [ABSTRACT FROM AUTHOR]

• The LDI proxy is calibrated for the tropics using South China Sea surface sediments. • LDI values are negatively correlated with SST at temperatures above 27 °C. • This new LDI calibration is well correlated with archaeal lipid temperature proxies. The Long-chain Diol Index (LDI) is a palaeotemperature proxy applied to marine sediments up to Miocene in age. Recent studies have revealed that the LDI-inferred temperature yields significant errors in waters >27 °C. This necessitates further assessment of the performance of the LDI proxy in high-temperature marine regimes. For this purpose, we collected 58 surface sediment samples from the tropical South China Sea (SCS), where annual sea surface temperature (SST) ranges from 24 °C to 29 °C. The original LDI calibration yields temperatures <27 °C for these samples, and the residual between the LDI-inferred temperature and the measured SST (ΔT) increases (to >4 °C) as SST increases. This ΔT, or mis-calibration, is significantly correlated with the measured SST as the temperature increases above 27 °C. This relationship also exists in sediment trap data. We therefore re-calibrated the LDI-inferred temperature to generate a new relationship that can be applied to environments with SST >27 °C, which is beyond the range of the original LDI proxy. Both the recalibrated LDI and, for comparison, archaeal lipid temperature proxies were applied in the high-temperature SCS; the improved correlation shows the LDI recalibration could be applied to palaeo-records from tropical oceans. [ABSTRACT FROM AUTHOR]

Bivalve shells are among the most promising archives for high-resolution seawater temperature reconstructions. However, despite major research advances in bivalve sclerochronology over the past decades, estimating water temperature from shells remains a challenging task. This is largely because the most frequently used and widely accepted temperature proxy in bivalves, i.e., the shell oxygen isotope (δ18O shell) value, also requires knowledge of changes in δ18O of the water (δ18O water) in which the bivalve lived, which is rarely available for ancient environments. According to a few recent studies, the size and shape of individual biomineral units (BMUs) of the shell ultrastructure may serve as an independent temperature proxy that is also less vulnerable to diagenetic changes than isotope chemical proxies. However, the crossed-lamellar ultrastructure, which occurs in ca. 90% of all mollusk species, has hitherto not been investigated. Here, we evaluate the potential use of morphological properties of the BMUs in Glycymeris bimaculata as a proxy for water temperature. For this purpose we introduce a suitable preparation technique (immersion for 2 m in 0.001 vol% formic acid followed by 20–30 m in 3.5 vol% H 2 O 2) and an automated image processing technique that tremendously speed up ultrastructure analysis (5 s versus one to 2 h image processing time with automated and manual methods, respectively) and increase the robustness of BMU measurements. Glycymeris is a particularly useful target taxon, because it is a cosmopolitan genus with evolutionary roots in the Upper Cretaceous, and some species of Glycymeris can attain a lifespan of more than two hundred years, which allows for long-term, high-resolution paleoclimate reconstructions. As in other previously studied ultrastructures, larger and more elongated BMUs formed in warmer water permitting temperature estimates with an error of 2.3 °C (1 σ). Since the new temperature proxy is unaffected by other environmental variables, including salinity, it can potentially be applied to (modern and fossil) specimens from brackish environments. Image 1 • Ultrastructure of Glycymeris bimaculata shells serves as temperature proxy (±2.3 °C). • Larger biominerals (nm-scale) form in warmer water. • New proxy works in brackish and saline nearshore environments. • New proxy potentially applicable to other mollusks with crossed-lamellar ultrastructure. • Automated image processing algorithms facilitate biomineral mapping. [ABSTRACT FROM AUTHOR]

• Distinctive distributions of 3-OH-FAs in marine surface sediments vs soils. • 16S rRNA analysis shows distinct bacterial populations in marine sediments. • We propose RAN 13 as a new proxy for sea surface temperature reconstruction. 3-Hydroxy fatty acids (3-OH-FAs), derived from Gram-negative bacterial outer membranes, have received recent attention for their potential as new terrestrial pH and temperature proxies for palaeoclimate studies. However, it is not known whether 3-OH-FA based proxies can be developed and applied to the marine environment. Here we analyze 3-OH-FAs from a latitudinal transect of marine surface sediments from the North Pacific Ocean (12°N to 61°N with a annual mean sea surface temperature (SST) range of 28.1–1.3 °C). The results show that distributions of 3-OH-FAs in marine sediments yield overall higher abundances of anteiso 3-OH-FA homologues compared to soils. Furthermore, 16S rRNA gene sequencing of the marine sediments and soils shows the Gram-negative bacterial community is dominated by Proteobacteria (ca. 94%) at the phylum level. In contrast, in regional soils the Gram-negative bacterial community is more diverse with significant contributions from Proteobacteria (ca. 50%), Acidobacteria (ca. 24%), Verrucomicrobia (6%), Bacteroidetes (6%) and other phyla. These distinct genomic and molecular differences suggest distinctly different aggregate compositions of bacteria that produce 3-OH-FAs in the marine realm vs soils. Moreover, we find that the ratio of anteiso to normal C 13 3-OH-FA (RAN 13) measured in surface sediments is highly correlated with annual mean SST throughout the temperature transect. When applied to a short sediment core from the East China Sea, the SST changes reconstructed by the RAN 13 proxy are comparable to instrumental SST data. These findings demonstrate that RAN 13 and potentially other, so far undiscovered, proxies based on 3-OH-FAs have potential for environmental and palaeoclimate applications in marine environments. [ABSTRACT FROM AUTHOR]

Stable isotope ratios in patelloid limpets of the genus Patella have been established as proxies for coastal environmental change at sub-monthly resolution along the eastern North Atlantic and Mediterranean Sea. Nacella deaurata (Gmelin 1791) and N. magellanica (Gmelin 1791) are common intertidal species of patelloid limpets inhabiting the coast of Tierra del Fuego, Argentina/Chile and are commonly found in Holocene archaeological deposits. Here, we examine oxygen and carbon isotope ratios (δ18O shell and δ13C shell , respectively) of modern specimens of N. deaurata and N. magellanica to test the hypotheses that: 1) they form their shells in isotopic equilibrium with ambient water; and 2) prominent growth lines form annually. Based on growth margin analysis of δ18O shell values, we identified a positive offset of 1.3 ± 0.4‰ (N. deaurata) and 1.3 ± 0.3‰ (N. magellanica) from expected equilibrium, similar to other patelloid limpets. Because the offset is relatively consistent between observed and expected values, it can be taken into account to reliably reconstruct growth temperature. Seawater temperature estimated from oxygen isotope time series data falls within the observed range. Thus, N. deaurata and N. magellenica shells serve as reliable proxy archives of seasonal variation in coastal seawater temperature. Time series of δ13C shell values do not vary seasonally in all shells; hence, the influence on its variation requires further study. The timing of prominent growth lines contextualized by the δ18O shell time series form twice a year and therefore cannot be used to estimate lifespan. Future isotopic analysis of archaeological Nacella shells can potentially provide much needed information about Holocene climate change at sub-monthly resolution from high-latitude South American locations, and contribute to our understanding of human behavior and human-climate interactions. • Nacella spp. show disequilibrium in oxygen isotope ratios • A constant ~1‰ offset from expected δ18O values exists like other patelloid species • SST can be reliably estimated after taking the constant δ18O offset into account • Prominent growth lines form twice a year in both species • Prominent growth lines cannot be used to estimate lifespan in Nacella shells [ABSTRACT FROM AUTHOR]