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Ocean acidification (OA), the decrease in surface ocean pH and seawater saturation state with respect to carbonate minerals (Ω), is expected to increase carbonate mineral dissolution. However, the influence of OA on carbonate dissolution has been largely neglected despite evidence that it is more sensitive to OA than calcification. Increases in the rate of carbonate dissolution could have severe impacts for ecosystems such as coral reefs, which rely on the accumulation of carbonate structures and substrates to exist. At present, dissolution rates of bulk shallow biogenic carbonate sediments are largely unknown and laboratory dissolution rates exceed in situ rates by orders of magnitude. The goal of this study was to develop a better understanding of the drivers and controls of bulk carbonate sediment dissolution in coral reef environments. Based on results from in situ benthic chambers and laboratory free-drift experiments of bulk biogenic carbonate sediments from global locations, dissolution rates were found to be primarily controlled by organic matter decomposition, but significantly influenced by the overlying seawater carbonate chemistry and the solubility of the most soluble mineral phase in the sediments. Shallow carbonate dissolution will therefore be enhanced via ocean acidification, increased respiration, or a combination of these processes. The sensitivity of bulk sediment dissolution rates to changes in Ω was not related to median grain size or mineralogy, but may be attributed to organic coatings on sediment grains. Dissolution rates in bulk sediments increased ~2-3-fold when these coatings were removed, suggesting that they act as a protective barrier that limits direct interaction of seawater with the mineral surface, thus inhibiting dissolution. On the ecosystem scale, carbonate dissolution was inferred from calcium anomalies measured using a novel spectrophotometric titration system and confirms seasonal and inter-annual trends in reef biogeochemical processes based on parallel alkalinity measurements. However, calcium measurements may be best employed in environments where multiple processes significantly influence alkalinity or Mg-calcites are precipitating and dissolving. Although many questions remain, this work has elucidated certain key drivers and controls of shallow carbonate sediment dissolution and how they may respond to a rapidly changing ocean.

Modeling marine low clouds and fog in coastal environments remains an outstanding challenge due to the inherently complex ocean–land–atmosphere system. This is especially important in the context of global circulation models due to the profound radiative impact of these clouds. This study utilizes aircraft and satellite measurements, in addition to numerical simulations using the Weather Research and Forecasting (WRF) Model, to examine three well-observed coastally trapped disturbance (CTD) events from June 2006, July 2011, and July 2015. Cloud water-soluble ionic and elemental composition analyses conducted for two of the CTD cases indicate that anthropogenic aerosol sources may impact CTD cloud decks due to synoptic-scale patterns associated with CTD initiation. In general, the dynamics and thermodynamics of the CTD systems are well represented and are relatively insensitive to the choice of physics parameterizations; however, a set of WRF simulations suggests that the treatment of model physics strongly influences CTD cloud field evolution. Specifically, cloud liquid water path (LWP) is highly sensitive to the choice of the planetary boundary layer (PBL) scheme; in many instances, the PBL scheme affects cloud extent and LWP values as much as or more than the microphysics scheme. Results suggest that differences in the treatment of entrainment and vertical mixing in the Yonsei University (nonlocal) and Mellor–Yamada–Janjić (local) PBL schemes may play a significant role. The impact of using different driving models—namely, the North American Mesoscale Forecast System (NAM) 12-km analysis and the NCEP North American Regional Reanalysis (NARR) 32-km products—is also investigated.

Due to processes that are poorly understood, the arctic/subarctic region is currently warming at approximately twice the rate of the rest of the globe, and these regional changes may in turn have important consequences on global climate. The Bering Sea is an ideal location to study the relationship between sea ice distribution, ocean circulation, and biological productivity, which are all thought to be components of important interactions that both respond to and influence climate changes on regional (North Pacific) to global scales. Geologic records are essential for understanding and predicting future oceanic and climatic changes, but most previous studies of Bering Sea and North Pacific climate and oceanic conditions were limited by short records that only spanned one glacial-interglacial climate cycle (~100 kyr). This dissertation presents new geochemical and sedimentological records of oceanic and climatic conditions over the past 1.2 Myr using sediment cores from Integrated Ocean Drilling Program Site U1342 (54.83N, 176.92E, 818 m water depth) in the Bering Sea, providing an unprecedented opportunity to examine trends over multiple glacial-interglacial cycles. Long benthic foraminiferal stable isotope records from Site U1342 provide the first evidence of an important recurring relationship in which extremely cold glacial conditions lead to enhanced Bering Sea ice extent and enhanced local formation of North Pacific Intermediate Water (NPIW), the water mass primarily associated with large-scale North Pacific circulation and heat transport. These results contradict model predictions for weaker NPIW formation during extreme glacial conditions and show that North Pacific and North Atlantic circulation acted in phase on glacial-interglacial timescales. Furthermore, new records of nitrate utilization based on nitrogen isotopes demonstrate that glacial climates were consistently associated with enhanced physical stratification in the Bering Sea, which resulted in increased utilization of nutrients by phytoplankton and a reduction in the carbon dioxide released from the ocean to the atmosphere. Finally, multiple new records that demonstrate high productivity during intervals of laminated sediments, which represent brief anoxic events, indicate that interglacial climates precondition the Bering Sea for rapid oceanic and biological change.

The decrease in delta C-13 of dissolved inorganic carbon (delta C-13(DIC)) owing to uptake of anthropogenic CO2 (the oceanic C-13 Suess effect) in the Southeastern Indian Ocean over the last decade was calculated using an extended multiparameter linear regression technique. Samples collected on the CROCCA-2S (Coring to Reconstruct Ocean Circulation and Carbon Dioxide Across 2 Seas) cruise in November-December 2018 were compared to samples from the CLIVAR (Climate and Ocean: Variability, Predictability, and Change) and OISO (Ocean Indien Service d'Observation) programs from 2007 to 2009. Surface ocean delta C-13(DIC) decreased by an average of -0.53 +/- 0.04 parts per thousand across this period, at an average rate of -0.053 +/- 0.004 parts per thousand per year. This rate of delta C-13(DIC) change is an increase from -0.021 +/- 0.024 parts per thousand per year between 1994 and 2008. We find that the interior water mass most impacted by the oceanic C-13 Suess effect between 2008 and 2018 was Subantarctic Mode Water (SAMW), within which delta C-13(DIC) decreased by -0.044 +/- 0.002 parts per thousand per year. Using previously published relationships between the oceanic C-13 Suess effect and anthropogenic carbon, we estimate the annual storage of anthropogenic carbon within SAMW in the southeastern Indian Ocean has increased from similar to 2.0 +/- 0.2 mu mol/kg per year between 1994 and 2008 to 5.5 +/- 0.6 mu mol/kg per year between 2008 and 2018.

Although dissolved concentrations of germanium (Ge) and silicon (Si) in modern seawater are tightly correlated, uncertainties still exist in the modern marine Ge cycle. Germanium stable isotope systematics in marine systems should provide additional constraints on marine Ge sources and sinks, however the low concentration of Ge in seawater presents an analytical challenge for isotopic measurement. Here, we present a new method of pre-concentration of inorganic Ge from seawater which was applied to measure three Ge isotope profiles in the Southern Ocean and deep seawater from the Atlantic and Pacific Oceans. Germanium isotopic measurements were performed on Ge amounts as low as 2.6 ng using a double-spike approach and a hydride generation system coupled to a MC-ICP-MS. Germanium was co-precipitated with iron hydroxide and then purified through anion-exchange chromatography. Results for the deep (i.e. > 1000 m depth) Pacific Ocean off Hawaii (nearby Loihi Seamount) and the deep Atlantic off Bermuda (BATS station) showed nearly identical δ74/70Ge values at 3.19 ± 0.31 ‰ (2SD, n = 9) and 2.93 ± 0.10 ‰ (2SD, n = 2), respectively. Vertical distributions of Ge concentration and isotope composition in the deep Southern Ocean for water depth > 1300 m yielded an average δ74/70Ge = 3.13 ± 0.25 ‰ (2SD, n = 14) and Ge/Si = 0.80 ± 0.09 mol/mol (2SD, n = 12). Significant variations in δ74/70Ge, from 2.62 to 3.71 ‰, were measured in the first 1000 m in one station of the Southern Ocean near Sars Seamount in the Drake Passage, with the heaviest values measured in surface waters. Isotope fractionation by diatoms during opal biomineralization may explain the enrichment in heavy isotopes for both Ge and Si in surface seawater. However, examination of both oceanographic parameters and δ74/70Ge values suggest also that water mass mixing and potential contribution of shelf-derived Ge also could contribute to the variations. Combining these results with new Ge isotope data for deep-sea sponges sampled nearby allowed us to determine a Ge isotope fractionation factor of -0.87 ± 0.37 ‰ (2SD, n = 12) during Ge uptake by sponges. Although Ge has long been considered as a geochemical twin of Si, this work underpins fundamental differences in their isotopic behaviors both during biomineralization processes and in their oceanic distributions. This suggests that combined with Si isotopes, Ge isotopes hold significant promise as a complementary proxy for delineating biological versus source effects in the evolution of the marine silicon cycle through time.

The Ocean Observatories Initiative (OOI) is an integrated network that enables scientific investigation of interlinked physical, chemical, biological and geological processes throughout the global ocean. With near real-time data delivery via a common Cyberinfrastructure, the OOI instruments two contrasting ocean systems at three scales. The Regional Cabled Array instruments a tectonic plate and overlying ocean in the northeast Pacific, providing a permanent electro-optical cable connecting multiple seafloor nodes that provide high power and bandwidth to seafloor sensors and moorings with instrumented wire crawlers, all with speed-of-light interactive capabilities. Coastal arrays include the Pioneer Array, a relocatable system currently quantifying the New England shelf-break front, and the Endurance Array, a fixed system off Washington and Oregon with connections to the Regional Cabled Array. The Global Arrays host deep-ocean moorings and gliders to provide interdisciplinary measurements of the water column, mesoscale variability, and air-sea fluxes at critical high latitude locations. The OOI has unique aspects relevant to the international ocean observing community. The OOI uses common sensor types, verification protocols, and data formats across multiple platform types in diverse oceanographic regimes. OOI observing is sustained, with initial deployment in 2013 and 25 years of operation planned. The OOI is distributed among sites selected for scientific relevance based on community input and linked by important oceanographic processes. Scientific highlights include real-time observations of a submarine volcanic eruption, time-series observations of methane bubble plumes from Southern Hydrate Ridge off Oregon, observations of anomalous low-salinity pulses off Oregon, discovery of new mechanisms for intrusions of the Gulf Stream onto the shelf in the Middle Atlantic Bight, documentation of deep winter convection in the Irminger Sea, and observations of extreme surface forcing at the most southerly surface mooring in the world ocean.

The variability of sea surface Total Alkalinity (TA) and sea surface Total Inorganic Carbon (C T ) is examined using all available data in the western tropical Atlantic (WTA: 20°S-20°N, 60°W-20°W). Lowest TA and C T are observed for the region located between 0°N-15°N/60°W-50°W and are explained by the influence of the Amazon plume during boreal summer. In the southern part of the area, 20°S-10°S/40°W-60°W, the highest values of TA and C T are linked to the CO 2 –rich waters due to the equatorial upwelling, which are transported by the South Equatorial Current (SEC) flowing from the African coast to the Brazilian shore. An increase of C T of 0.9 ± 0.3 μmol kg −1 yr −1 has been observed in the SEC region and is consistent with previous published estimates. A revised C T -Sea Surface Salinity (SSS) relationship is proposed for the WTA to take into account the variability of C T at low salinities. This new C T -SSS relationship together with a published TA-SSS relationship allow to calculate p CO 2 values that compare well with observed p CO 2 (R 2 = 0.90).

Vertical distributions of iron (Fe) concentrations and isotopes were determined in the total dissolvable and dissolved pools in the water column at three coastal stations located along the Peruvian margin, in the core of the Oxygen Minimum Zone (OMZ). The shallowest station 121 (161 m total water depth) was characterized by lithogenic input from the continental plateau, yielding concentrations as high as 456 nM in the total dissolvable pool. At the 2 other stations (stations 122 and 123), Fe concentrations of dissolved and total dissolvable pools exhibited maxima in both surface and deep layers. Fe isotopic composition (δ56Fe) showed a fractionation toward lighter values for both physical pools throughout the water column for all stations with minimum values observed for the surface layer (between -0.64 and -0.97 ‰ at 10 - 20 m depth) and deep layer (between -0.03 to -1.25 ‰ at 160 - 300 m depth). An Fe isotope budget was established to determine the isotopic composition of the particulate pool. We observed a range of δ56Fe values for particulate Fe from + 0.02 to -0.87 ‰, with lightest values obtained at water depth above 50 m. Such light values in the both particulate and dissolved pools suggest sources other than atmospheric dust deposition in the surface ocean, including lateral transport of isotopically light Fe. Samples collected at station 122 closest to the sediment show the lightest isotope composition in the dissolved and the particulate pools (-1.25 and -0.53 ‰ respectively) and high Fe(II) concentrations (14.2 ± 2.1 nM) consistent with a major reductive benthic Fe sources that is transferred to the ocean water column. A simple isotopic model is proposed to link the extent of Fe(II) oxidation and the Fe isotope composition of both particulate and dissolved Fe pools. This study demonstrates that Fe isotopic composition in OMZ regions is not only affected by the relative contribution of reductive and non-reductive shelf sediment input but also by seawater-column processes during the transport and oxidation of Fe from the source region to open seawater.

The size partitioning of dissolved Fe (dFe 56 Fe of +1.3‰ to +1.5‰) relative to dFe (δ 56 Fe~+0.5‰) in the surface ocean where sFe and cFe cycle independently, and identical sFe and dFe isotope ratios below 250 m where sFe and cFe are constantly partitioned and exchanged.

The ocean is currently absorbing excess carbon from anthropogenic emissions, leading to reduced seawater-pH (termed ‘ocean acidification’). Instrumental records of ocean acidification are unavailable from well-ventilated areas of the deep ocean, necessitating proxy records to improve spatio-temporal understanding on the rate and magnitude of deep ocean acidification. Here we investigate boron, carbon, and oxygen isotopes on live-collected deep-sea bamboo corals (genus Keratoisis) from a pHtot range of 7.5–8.1. These analyses are used to explore the potential for using bamboo coral skeletons as archives of past deep-sea pH and to trace anthropogenic acidification in the subsurface North Atlantic Ocean (850–2000 m water depth). Boron isotope ratios of the most recently secreted calcite of bamboo coral skeletons are close to the calculated isotopic composition of borate anion in seawater (δ11Bborate) for North Atlantic corals, and 1–2‰ higher than δ11Bborate for Pacific corals. Within individual coral skeletons, carbon and oxygen isotopes correlate positively and linearly, a feature associated with vital effects during coral calcification. δ11B variability of 0.5–2‰ is observed within single specimens, which exceeds the expected anthropogenic trend in modern North Atlantic corals. δ11B values are generally elevated in Pacific corals relative to δ11Bborate, which may reflect pH-driven physiological processes aiding coral calcification in environments unfavorable for calcite precipitation. Elevated δ11B values are also observed proximal to the central axis in multiple Atlantic and Pacific specimens, relative to δ11Bborate, which might reflect ontogenetic variability in calcification rates. Although the observed boron isotope variability is too large to resolve the present anthropogenic ocean acidification signal at the studied depths in the North Atlantic (∼0.03–0.07 pH units), pH changes ⩾0.1 units might still be reconstructed using δ11B measurements in bamboo corals.

Particles influence trace element and isotope (TEI) cycles through both their elemental composition and fate and their role on the partitioning of dissolved elements through scavenging and dissolution. Because of their complex compositions, a diverse suite of methods is required to analyze marine particles. Here we review some of the varied approaches used to study particle composition, speciation and fate. We focus on high throughput analytical methods that are useful for the international GEOTRACES program, and we also describe new spectroscopic techniques that are now being applied to study the spatial distribution and chemical speciation of TEIs in marine particles.

The subtropical ocean, exposed to evaporation excess over precipitation, is characterized by regional sea surface salinity maxima (SSS-max). Ocean circulation and mixing processes inject freshwater, establishing a quasi-steady state, though imbalances across the time spectrum result in periods of increasing and decreasing SSS-max. The integrated effect of the array of atmospheric and oceanic forces governing sea surface salinity is shaped by the specific regional ocean basin configuration as well as their coupling to the global ocean system, resulting in SSS-max patterns and locations that display marked differences between the subtropical regimes. We provide a brief description of the SSS-max characteristics of the five subtropical regimes and present aspects of their regional settings that may account for their dissimilarities.

The eruptive process that took place in October 2011 in the submarine volcano Tagoro off the Island of El Hierro and the subsequent degasification stage, five months later, have increased the concentration of TdFe(II) (Total dissolved iron(II)) in thewaters nearest to the volcanic edifice. In order to detect any variation in concentrations of TdFe(II) due to hydrothermal emissions, three cruiseswere carried out two years after the eruptive process in October 2013,March 2014 andMay 2015. The results fromthese cruises confirmed important positive anomalies in TdFe(II), which coincided with negatives anomalies in pHF,is (pH in free scale, at in situ conditions) located in the proximity of themain cone. Maximumvalues in TdFe(II) both at the surface, associated to chlorophyll a maximum, and at the sea bottom, were also observed, showing the important influence of organic complexation and particle re-suspension processes. Temporal variability studies were carried out over periods ranging from hours to days in the stations located over themain and two secondary cones in the volcanic edifice with positive anomalies in TdFe(II) concentrations and negative anomalies in pHF,is values. Observations showed an important variability in both pHF,is and TdFe(II) concentrations, which indicated the volcanic area was affected by a degasification process that remained in the volcano after the eruptive phase had ceased. Fe(II) oxidation kinetic studies were also undertaken in order to analyze the effects of the seawater properties in the proximities of the volcano on the oxidation rate constants and t1/2 (half-life time) of ferrous iron. The increased TdFe(II) concentrations and the low associated pHF,is values acted as an important fertilization event in the seawater around the Tagoro volcano at the Island of El Hierro providing optimal conditions for the regeneration of the area., SI

The Paleocene-Eocene Thermal Maximum (PETM) has been associated with the release of several thousands of petagrams of carbon (Pg C) as methane and/or carbon dioxide into the ocean-atmosphere system within ~10 kyr, on the basis of the co-occurrence of a carbon isotope excursion (CIE), widespread dissolution of deep sea carbonates, and global warming. In theory, this rapid carbon release should have severely acidified the surface ocean, though no geochemical evidence has yet been presented. Using boron-based proxies for surface ocean carbonate chemistry, we present the first observational evidence for a drop in the pH of surface and thermocline seawater during the PETM. Planktic foraminifers from a drill site in the North Pacific (Ocean Drilling Program Site 1209) show a ~0.8‰ decrease in boron isotopic composition (δ11B) at the onset of the event, along with a 30–40% reduction in shell B/Ca. Similar trends in δ11B are present in two lower-resolution records from the South Atlantic and Equatorial Pacific. These observations are consistent with significant, global acidification of the surface ocean lasting at least 70 kyr and requiring sustained carbon release. The anomalies in the B records are consistent with an initial surface pH drop of ~0.3 units, at the upper range of model-based estimates of acidification.

NDSEG; NSF Chemical Oceanography program [OCE-0751525]; Coastal Ocean Institute; Ocean and Climate Change Institute at Woods Hole Oceanographic Institution

Uncertainties surround the relationship between salinity and the stable isotopic composition of seawater, largely due to a dearth of modern seawater isotope data. Here we report 191 new, paired measurements of salinity and seawater oxygen isotopes (δ¹⁸O_sw) taken from the central tropical Pacific in May 2012, from the surface to 4600 m depth. We observe significant correlations between δ¹⁸O_sw and salinity across the study region, with slopes ranging from 0.23 to 0.31‰/psu for the mixed layer, and 0.35–0.42‰/psu for waters between the mixed layer and 500 m depth. When considering δ¹⁸O_sw–salinity across averages of individual water masses in the region, slopes range from 0.21 to 0.40‰/psu, albeit with appreciable scatter. Surface salinity and δ¹⁸O_sw data corresponding to the North Equatorial Countercurrent are significantly higher than previously observed, which we attribute to a weak westerly current and dry conditions in the region during the May 2012 cruise. Subsurface (80–500 m) salinity values from 2012 are significantly lower than corresponding values from pre-existing regional data, highlighting a different latitudinal sampling distribution, while subsurface δ¹⁸O_sw is not significantly different. Thus, in May 2012, δ¹⁸O_sw in this region could not be used to distinguish between subsurface water masses of different salinities. Unlike other regions where the surface ‘freshwater endmember’ is close to the δ¹⁸O value of regional precipitation, the freshwater endmember implied by our dataset (− 10.38‰) is consistent with a strong evaporative influence. Paired δ¹⁸O–δD values of precipitation and surface seawaters have similar slopes (5.0, 5.1), and relatively low intercepts (1.4, 0.8) indicating isotopic variability in both reservoirs is also partly controlled by evaporation.

The ratio of unsupported protactinium-231 to thorium-230 in marine sediments, (Pa/Th)xs, is potentially sensitive to several processes of oceanographic and climatological interest: deep ocean circulation, marine biological productivity (as it relates to total particle flux) and particle composition (specifically, biogenic opal and authigenic Mn). In order to attribute variations in (Pa/Th)xs observed in sediment records to changes in specific processes through time, a better understanding of the chemical cycling of these elements in the modern ocean is necessary. To this end, a survey was undertaken of (Pa/Th)xs in surface sediments from the subarctic Pacific (SO202-INOPEX expedition) in combination with a Pacific-wide compilation of published data. Throughout the Pacific, (Pa/Th)xs is robustly correlated with the opal content of sediments. In the North and equatorial Pacific, simultaneous positive correlations with productivity indicators suggest that boundary scavenging and opal scavenging combine to enhance the removal of Pa in the eastern equatorial Pacific and subarctic Pacific. Deep ocean water mass ageing (>3.5 km>3.5 km) associated with the Pacific overturning appears to play a secondary role in determining the basin scale distribution of (Pa/Th)xs. A basin-wide extrapolation of Pa removal is performed which suggests that the Pacific Pa budget is nearly in balance. We hypothesize that through time (Pa/Th)xs distributions in the Pacific could define the evolving boundaries of contrasting biogeographic provinces in the North Pacific, while the influence of hydrothermal scavenging of Pa potentially confounds this approach in the South Pacific.

Despite its enormous extent and importance for global climate, the South Pacific has been poorly investigated in comparison to other regions with respect to chemical oceanography. Here we present the first detailed analysis of dissolved radiogenic Nd isotopes (eNd) and rare earth elements (REEs) in intermediate and deep waters of the mid-latitude (∼40°S) South Pacific along a meridional transect between South America and New Zealand. The goal of our study is to gain better insight into the distribution and mixing of water masses in the South Pacific and to evaluate the validity of Nd isotopes as a water mass tracer in this remote region of the ocean. The results demonstrate that biogeochemical cycling (scavenging processes in the Eastern Equatorial Pacific) and release of LREEs from the sediment clearly influence the distribution of the dissolved REE concentrations at certain locations. Nevertheless, the Nd isotope signatures clearly trace water masses including AAIW (Antarctic Intermediate Water) (average eNd = −8.2 ± 0.3), LCDW (Lower Circumpolar Deep Water) (average eNd = −8.3 ± 0.3), NPDW (North Pacific Deep Water) (average eNd = −5.9 ± 0.3), and the remnants of NADW (North Atlantic Deep Water) (average eNd = −9.7 ± 0.3). Filtered water samples taken from the sediment–water interface under the deep western boundary current off New Zealand suggest that boundary exchange processes are limited at this location and highlight the spatial and temporal variability of this process. These data will serve as a basis for the paleoceanographic application of Nd isotopes in the South Pacific.

An Advanced Laser Fluorometer (ALF) capable of discriminating several phytoplankton pigment types was utilized in conjunction with microscopic data to map the distribution of phytoplankton communities in the Amazon River plume in May–June-2010, when discharge from the river was at its peak. Cluster analysis and Non-metric Multi-Dimensional Scaling (NMDS) helped distinguish three distinct biological communities that separated largely on the basis of salinity gradients across the plume. These three communities included an ‘‘estuarine type’’ comprised of a high biomass mixed population of diatoms, cryptophytes and green-water Synechococcus spp. located upstream of the plume, a ‘‘mesohaline type’’ made up largely of communities of Diatom-Diazotroph Associations (DDAs) and located in the northwestern region of the plume and an ‘‘oceanic type’’ in the oligotrophic waters outside of the plume made up of Trichodesmium and Synechococcus spp. Although salinity appeared to have a substantial influence on the distribution of different phytoplankton groups, ALF and microscopic measurements examined in the context of the hydro-chemical environment of the river plume, helped establish that the phytoplankton community structure and distribution were strongly controlled by inorganic nitrate plus nitrite (NO3 +N O 2) availability whose concentrations were low throughout the plume. Towards the southern, low-salinity region of the plume, NO3 +N O 2 supplied by the onshore flow of subsurface (80 m depth) water, ensured the continuous sustenance of the mixed phytoplankton bloom. The large drawdown of SiO3 and PO4 associated with this ‘‘estuarine type’’ mixed bloom at a magnitude comparable to that observed for DDAs in the mesohaline waters, leads us to contend that, diatoms, cryptophytes and Synechococcus spp., fueled by the offshore influx of nutrients also play an important role in the cycling of nutrients in the Amazon River plume.

The biogeochemical cycle of zinc (Zn) in the South Atlantic, at 40°S, was investigated as part of the UK GEOTRACES program. To date there is little understanding of the supply of Zn, an essential requirement for phytoplankton growth, to this highly productive region. Vertical Zn profiles displayed nutrient-like distributions with distinct gradients associated with the water masses present. Surface Zn concentrations are among the lowest reported for the world's oceans ( 2 = 0.97, n = 460). Our results suggest that the use of a global Zn-Si relationship would lead to an underestimation of dissolved Zn in deeper waters of the South Atlantic. By utilizing Si* and a new tracer Zn* our data indicate that the preferential removal of Zn in the Southern Ocean prevented a direct return path for dissolved Zn to the surface waters of the South Atlantic at 40°S and potentially the thermocline waters of the South Atlantic subtropical gyre. The importance of Zn for phytoplankton growth was evaluated using the Zn-soluble reactive phosphorus (SRP) relationship. We hypothesize that the low Zn concentrations in the South Atlantic may select for phytoplankton cells with a lower Zn requirement. In addition, a much deeper kink at ~ 500m in the Zn:SRP ratio was observed compared to other oceanic regions. Key Points Dissolved zinc biogeochemical cycle investigated in the South Atlantic Ocean ©2014. American Geophysical Union. All Rights Reserved.

Dissolved Th-232 is added to the ocean though the partial dissolution of lithogenic materials such as aerosol dust in the same way as other lithogenically sourced and more biologically important trace metals such as Fe. Oceanic Th-230, on the other hand, is sourced primarily from the highly predictable decay of dissolved U-234. The rate at which dissolved Th-232 is released by mineral dissolution can be constrained by a Th removal rate derived from Th-230:U-234 disequilibria, assuming steady-state. Calculated fluxes of dissolved Th-232 can in turn be used to estimate fluxes of other lithogenically sourced dissolved metals as well as the original lithogenic supplies, such as aerosol dust deposition, given the concentration and fractional solubility of Th (or other metals) in the lithogenic material. This method is applied to 7 water column profiles from the Innovative North Pacific Experiment (INOPEX) cruise of 2009 and 2 sites from the subtropical North Pacific. The structure of shallow depth profiles suggests rapid scavenging at the surface and at least partial regeneration of dissolved Th-232 at 100-200 m depth. This rapid cycling could involve colloidal Th generated during mineral dissolution, which may not be subject to the same removal rates as the more truly dissolved Th-230. An additional deep source of Th-232 was revealed in deep waters, most likely dissolution of seafloor sediments, and offers a constraint on dissolved trace element supply due to boundary exchange. (C) 2013 Elsevier B.V. All rights reserved.

The boron isotopic composition of biogenic carbonates has been used to reconstruct seawater pH and atmospheric pCO 2 on Pleistocene and Cenozoic timescales. Because of their excellent preservation and extensive fossil record throughout the Phanerozoic, brachiopods are a promising candidate for extending the boron isotope record as far back as the Cambrian. Here we present stable carbon, oxygen, and boron isotopic measurements of modern Terebratulid brachiopod calcite in comparison with environmental pH estimates calculated from oceanographic data. Geochemical transects along the length and depth of single shells confirm previously published trends in carbon and oxygen isotopic composition. In the outer surface (primary and outermost secondary layers), δ 11 B covaries with δ 13 C and δ 18 O, with more negative values in the outer and more positive values in the middle of the shell. However, δ 11 B deviates from δ 13 C and δ 18 O in the inner part of the secondary layer, where the δ 13 C and δ 18 O values are more positive and near equilibrium, whereas δ 11 B returns to more negative values. A comparison of different specimens of the species Terebratalia transversa (Sowerby, 1846) and Laqueus californianus (Kuster, 1844) microsampled from the middle part of the fibrous secondary layer demonstrates a clear correlation to ambient pH with a sensitivity similar to other empirical calibration curves for cultured planktic foraminifers, corals, and inorganic calcite. The relationship in other species is less clear and significantly offset, necessitating the use of a single species or a cross-calibration method with other species in paleo-pH reconstructions.

The present study aims to determine the concentrations of certain trace metals (Fe, Mn, Cr, Cu, Pb, Zn, Co, Ni, Ba, Sr, V and Rb) and to identify the possible sources of the trace metals with multivariate analyses and assess the metal contamination using the enrichment factor (EF) and geo-accumulation index (Igeo) from the two core samples taken from Pichavaram lagoon. Pichavaram mangrove is a dynamic intertidal environment lying in between Vellar and Coleroon estuaries in Cauvery delta along the east coast of India. High OM in the present study is noted in both core samples which are mainly controlled by productivity and sediment texture. The increase of trace metals concentrations was observed at lower intersects which indicates that the trace metals were reprecipitated around the redox boundaries. Further it signifies that the enrichment of metals in C1 core sample is closely related to the diagenetic. Factor 1 with significant positive loadings on Mud and good loadings on Fe and Mn suggests the associations of these metals with finer sediment fractions and aluminosilicates. These elements to be enriched in the clay fraction in both core samples. They are mainly related to anthropogenic inputs and reflect the complexing nature of the organic matter. Igeo studies confirm the contamination of the study area. Overall the study highlights significant anthropogenic contributions in terms of heavy metal pollution. Comparative data for normalized enrichment factors and the modified degree of contamination show that Pichavaram sediments have suffered significant systematic heavy metal contamination following catchment urbanization.

Trace metal micronutrients regulate primary production in oceanic surface waters, particularly those characterised as ‘high nutrient, low chlorophyll’, such as the Subantarctic Zone (SAZ). Our goal was to evaluate the distribution and biogeochemistry of Cd, Co, Cu, Ni and Zn in the upper 1000 m of this zone to the south of Australia during the SAZ-Sense Project (Jan–Feb 2007). 13 depth profiles were sampled for dissolved, labile metal measurements through subtropical and SAZ waters – west and east of Tasmania – and southward into the Polar Frontal Zone. We determined Cd from detection limit b4 pM to 900 pM, Co 5–43 pM, Cu 0.22–1.79 nM, Ni 2.51–7.31 nM and Zn b0.22–7.9. Throughout the study area, Cd, Cu and Ni correlated closely with the macronutrient phosphorus, but their depletion (relative to winter levels) in surface waters differed: Cd (64–>96%), Cu (2–35%), Ni (7–20%). The profile south of the Polar Front contrasted markedly with all others, having the lowest depletions in surface waters. Another discordancy was some anomalously high Cu concentrations in surface waters close to Tasmania. Co behaved as a recycled (nutrient) element correlatingwith P and Chl a in the top 200 m of the water column, but deeper it was different with a distinct subsurface peak. The characteristics of this peak suggested lateral supply of dissolved, labile Co from polar surface waters to lower-latitude ocean depths via Antarctic Intermediate Waters. Zn also typified a recycled micronutrient. It was loosely correlated with the macronutrient silicon—more strongly to the south and in the Polar Frontal Zone (PFZ). In the vicinity of the Subtropical Front to the east of Tasmania, dissolved Zn was decoupled from other micro- and macro-nutrients. Its irregular distribution suggested this region's dynamic eddy field and possibly variable supply and a phytoplankton community dominated by non-diatom species as influential factors. Distributions of Cd, Cu, Ni and Co were much more uniform in the vicinity of the Subtropical Front (only dissolved Fe data from SAZ-Sense exemplified similar patchiness in distribution as Zn), distinguished solely by being either side of the Front, in subtropical or subantarctic waters. These new data for Cd, Co, Cu, Ni and Zn improve scant coverage for them in the Australian sector of the Southern Ocean, and provide a basis for linking their distribution to regional primary productivity and variations in phytoplankton community structure.

Massive amounts of 13C-depleted carbon rapidly entered the ocean more than once during the Early Paleogene, providing a geological framework for understanding future perturbations in carbon cycling ...

The Kerguelen ocean and plateau compared study (KEOPS) examined the origin of elevated phytoplankton biomass in naturally iron-fertilized waters over the Kerguelen plateau during midsummer (January–February 2005). We report sinking particle characteristics determined from image analysis of thousands of individual particles collected in viscous polyacrylamide gels placed in free-drifting sediment traps at two sites: a high phytoplankton biomass site over the central plateau (A3) and a moderate biomass site at its periphery (C5). The particles were divided into three types (1) oval fecal pellets, (2) cylindrical fecal pellets, and (3) aggregates. The aggregates were most abundant and mainly consisted of agglomerations of the cylindrical fecal pellets. Conversion of the pellet and aggregate volumes to carbon contents suggests export fluxes of 50–60 mg C m22 d21 at 100-m depth, in reasonable agreement with independent estimates from carbon and 234Th measurements. Our observation that the majority of the particle flux was processed through the heterotrophic foodweb contrasts with the results of artificial iron-fertilization experiments and with models for export from productive diatomdominated waters that emphasize direct export of phytoplankton detritus. The KEOPS results may offer more appropriate scaling for the response of ecosystem structure and carbon export to persistent iron fertilization in the Southern Ocean.

Bioactive trace metals play a significant role as micronutrients in the ocean and therefore it is important to evaluate their sources. Submarine groundwater discharge (SGD) has been recognized as an input of trace metals to the coastal sea. Here, we investigated the significance of SGD as a source of dissolved trace metals (dTM) to the coastal sea in a regional area such as the North Western (NW) Mediterranean Sea. We analysed dTM concentrations in SGD end-members and incorporate data on SGD dTM concentrations and water flows reported in previous studies carried out in this area, to estimate the following ranges of SGD-driven dTM fluxes (in 10 mol y): Cd: 0.0007–0.03, Co: 0.004–0.11, Cu: 0.09–1.9, Fe: 1.8–29, Ni: 0.09–1.9, Pb: 0.002–0.06, Zn: 0.38–12. These fluxes were compared to dTM fluxes from riverine discharge and atmospheric deposition, demonstrating that SGD is a major source of dTM to the NW Mediterranean Sea. Whilst riverine inputs are limited to the surrounding of river mouths and atmospheric fluxes are distributed throughout the whole basin mainly during sporadic depositional events, SGD represents a permanent, albeit seasonally variable, source of metals to most of the coastal areas. SGD-driven dTM inputs may be even more significant, in relative terms, in other coastal regions of the Mediterranean Sea where rivers are scarce, as it is the case of the African coast and many islands. This study highlights the relevance of SGD as a source of dTM to the Mediterranean Sea and the need of its consideration in the calculation of metal budgets in the basin and in the investigation of biogeochemical cycles in coastal areas., This project has been partially funded by the European Union Seventh Framework Programme through the MetTrans Initial Training Network, Marie Curie Actions, which also provide financial support through a PhD fellowship to G.T. (EU FP7-People-2011-ITN-290336). Support provided by the Generalitat de Catalunya to MERS (2014 SGR – 1356) is also acknowledged. V.R. acknowledges financial support from the European Union's FP7 (Marie Curie Actions PCOFUND-GA-2013-609102), through the PRESTIGE programme coordinated by Campus France. The Spanish Government (MINECO) is acknowledged for support to E.G-S through a post-doctoral grant (FPDI-2013-15660) and support of ECOALFACS project (CTM2009-09581) to the ICM-CSIC. This research is also a contribution to the ANR @RAction chair (ANR-14-ACHN-0007-01) and Labex OT-Med (ANR-11-LABEX-0061) funded by the “Investissements d'Avenir” program through the A*MIDEX project (ANR-11-IDEX-0001-02) of the French National Research Agency (ANR).

Thesis: Ph. D., Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2016.

New isotope data obtained from relatively conformable, carbonate-rich strata of the Ediacaran Yangtze platform in South China reveal substantial δ 13 C variability. In platform sections, four negative δ 13 C anomalies with a nadir down to ≤−8‰ (PDB) are present in the interval between the cap carbonate level (∼635 Ma) and the Precambrian/Cambrian boundary (∼542 Ma), while in slope and basinal sections, δ 13 C values are negative through the entire Doushantuo Formation (∼635–551 Ma). If these δ 13 C values are close to their primary seawater signature, they imply a strong (≥10‰) surface-to-deep ocean δ 13 C gradient that is consistent with long-term deep ocean anoxia and the presence of a large dissolved organic carbon (DOC) reservoir. The two prominent negative δ 13 C excursions within the Doushantuo Formation above the cap carbonate level are associated with shoaling and local exposure of the platform. The anomalies may thus record remineralization of a large oceanic DOC pool via sulfate reduction that transferred 13 C-depleted carbon from the oceanic DOC reservoir to the surface ocean during regression. Inconsistencies in Ediacaran δ 13 C profiles globally and variations in South China in particular highlight the need for further evaluation of local departures in δ 13 C from an inferred average seawater signature.

We determine Southern Ocean diatom silicon isotopic signatures and compare them with the previously published data for dissolved silicic acid from the same locations. Five stations distributed along the WOCE SR-3 transect (Australian Sector of the Southern Ocean) in different biogeochemical provinces are presented: Polar Front and Inter-Polar Front Zones (PFZ–IPFZ), Southern Antarctic Zone (AZ-S), Seasonal Ice Zone (SIZ). Total (N0.4 μm), medium-sized (20–70 μm), and large diatoms (N70 μm) were sampled at 2–4 depths in the upper 150 m. Silicon isotopic compositions of biogenic silica (diatoms) and seawater were then measured by MC-ICP-MS, in dry plasma mode using external Mg doping. Results are expressed as δ 29 Si relative to the NBS28 standard. The isotopic composition of diatoms (δ 29 SiBSi) is generally homogeneous in the mixed layer and does not exhibit a systematic isotopic fractionation linked to a size effect. δ 29 SiBSi are always lighter than the ambient dissolved silicic acid signatures (δ 29 SiDSi), reflecting the preferential uptake of light isotopes by diatoms. A trend of lighter isotopic signatures southward is observed both in diatoms and seawater samples but the δ 29 SiBSi latitudinal gradient is much steeper. A diatom signature as low as −0.26‰ in the southernmost SIZ station strongly contrasts with the +0.65‰ signature measured on PFZ diatoms. The difference between the ambient dissolved silicic acid and diatom isotopic signatures, Δ 29 Si, strongly increases southward: from 0.4 in the PFZ up to 1.08‰ in the SIZ. This points toward occurrence of mixing events in the PFZ–IPFZ with diatoms not being under equilibrium with their surrounding water and/or, possible variation of the diatom–seawater equilibrium fractionation factor, 29 e. Apart from mixing, we found that the other parameters likely responsible of such variation are temperature, dissolved Si contents and, Si specific uptake and dissolution rates although at this stage none of these could be clearly recognized as the leading cause. Thorough examination of these parameters through in vitro experiments reflecting the extreme Southern Ocean conditions is needed to determine whether the observed latitudinal variation of Δ 29 Si reflects real variable fractionation or results from nonequilibrium or different time-scales recorded between dissolved and biogenic Si isotopic signatures. Our results also call for the development of more realistic models for describing short-term isotopic composition changes due to e.g. Si consumption, export

We examine progress towards a global view of oceanic export of particulate organic carbon (POC) and other nutrient elements (P, N, Si) from the surface (upper 100 m), through the subsurface, to the deep sea (>1000 m), focusing on syntheses published since 1999 and on the Joint Global Ocean Flux Study. Food-web structure is important, and surface and subsurface processes contribute similarly to determine the fraction of net primary production (NPP) reaching the deep sea. NPP by large cells generally favours high surface export of POC. Preferential remineralization of P and N (versus C) with depth is common, as is regional variation in subsurface POC flux attenuation. The role of mineral fluxes is complex. Annual mean fluxes of POC and minerals are correlated in global deep sediment trap records, but causality and the relative importance of different minerals depends on the assumptions made. Time-series observations at single sites can oppose the geographic trends, and their large seasonal variability in the contribution of POC to total flux is at odds with mechanistic models for POC transport by minerals. Despite generally positive correlations between biogenic carbonate and POC fluxes, the overall role of carbonate export is to decrease the transfer of carbon dioxide from the atmosphere to the ocean. Both autotrophs and heterotrophs produce minerals, and progress in separating these contributions is required for the deconvolution of mineral ballast and food-web effects. Many recent models suggest global surface POC export of 10 GTC/yr, despite widely varying biological complexity. This limits the usefulness of their prediction of ecosystem and carbon cycle responses to global change. Progress requires better observations for model validation, and more efforts to relate the models to the observed complexity, rather than to overly simplified global syntheses. We advocate more time-series stations targeting under-studied biogeochemical regions, development of automated in situ tools for study of the subsurface ocean, and increased emphasis on combining ecological and biogeochemical methods.

To evaluate the impact of modern glacier melting on the chemical enrichment of Antarctic coastal waters, we measured trace elements, including dissolved iron (Fe) and rare earth elements (REEs), together with dissolved inorganic nitrogen, phosphorous, silicate and dissolved organic carbon (DOC) in ice, snow and coastal seawater of Marian Cove in the northernmost part of Antarctica (62°S). There was an increase in the concentrations of Fe and other trace elements (Al, Mn, Cr, Ni, Co, Pb and REEs) between the bay mouth and the glacier valleys. Good correlations between salinity and these chemical elements indicate that the trend was mainly due to the influence of glacier meltwater (GMW). When the effect of GMW was quantified based on plots of its presence (average 5.7%) in the surface water of the cove, the concentrations of trace elements in seawater increased 18-fold for Fe, eight- to 10-fold for Al and Mn and up to four-fold for Cr, Ni, Co, Pb and REEs by GMW. However, the contribution of GMW to inorganic nutrients and DOC was negligible. The significance of GMW-borne REE contribution in this cove was further evidenced by middle REE enrichment in cove water. Our results suggest that the currently increasing glacier melting in Antarctica has a significant influence on the level of trace elements, particularly Fe, in cove water, which in turn may have a significant impact on the biogeochemistry of coastal seawater in Antarctica.Keywords: Iron; trace elements; rare earth elements; glacier melting; Antarctica; Marian Cove.(Published: 7 May 2015)Citation: Polar Research 2015, 34, 24289, http://dx.doi.org/10.3402/polar.v34.24289

We review Phanerozoic sea-level changes [543 million years ago (Ma) to the present] on various time scales and present a new sea-level record for the past 100 million years (My). Long-term sea level peaked at 100 ± 50 meters during the Cretaceous, implying that ocean-crust production rates were much lower than previously inferred. Sea level mirrors oxygen isotope variations, reflecting ice-volume change on the 10 4 - to 10 6 -year scale, but a link between oxygen isotope and sea level on the 10 7 -year scale must be due to temperature changes that we attribute to tectonically controlled carbon dioxide variations. Sea-level change has influenced phytoplankton evolution, ocean chemistry, and the loci of carbonate, organic carbon, and siliciclastic sediment burial. Over the past 100 My, sea-level changes reflect global climate evolution from a time of ephemeral Antarctic ice sheets (100 to 33 Ma), through a time of large ice sheets primarily in Antarctica (33 to 2.5 Ma), to a world with large Antarctic and large, variable Northern Hemisphere ice sheets (2.5 Ma to the present).

A physical–chemical–biological model of the Barents Sea is used to simulate the necessary conditions for primary production. The model is validated to in situ current measurements and temperature fields, and is compared with physical and chemical data from a section across the central part of the basin. The results show that the section is placed in a region with mesoscale variability and significant horizontal gradients. The results are therefore sensitive not only to forcing conditions, but to the growth of instabilities. Alternatives for interpreting the field data are suggested. An example of a “hidden” feature only a few grid points away suggests that a different approach combining the spatial and temporal variabilities may allow for a better validation.

Two cruises were conducted in the Pearl River Estuary (PRE) and adjacent coastal waters during July 1999 and 2000 to investigate spatial variation, transformation and degradation of amino'acids (AAs). Salinity, suspended sediments (SS), chl a, nutrients, dissolved organic carbon, particulate organic carbon, AAs, and hexosamines were measured and analyzed. Concentrations of particulate hydrolysable AAs (PHAAs), dissolved combined AAs and dissolved free AAs ranged from 0.41 to 12.6 mumol L-1, 1.1 to 4.0 mumol L-1 and 0.15 to 1.10 mumol L-1, respectively. AAs concentrations were low in waters of salinity 5 mug L-1 and SS 20 mg L-1) and reached the lowest values of 5.8 and 1.4 in sediments. In particular, the ratios of AAs/HAs, Glc-NH2/Gal-NH2 were low in the upper or northwest side of the estuary where turbidity was high. This indicated that these AAs were "old", likely due to resuspension of refractory organic matter from sediments or zooplankton grazing modification and bacterial reworking as the salt wedge advanced upstream near the bottom. Apparently, the dynamics of AAs in the PRE appeared to be governed by biological production processes and estuarine circulation in the estuary. As the chl a maximum developed downstream in the estuarine and coastal plume and the salt wedge moved upstream at the bottom, AAs increased and were subjected to sinking as particulates, grazing by zooplankton and reworking by bacterial activity. Sinking AAs would be transformed and modified in the lower layer, which would be brought back into the estuary in the salt wedge during the estuarine circulation. (C) 2004 Elsevier Ltd. All rights reserved.

This study provides a comprehensive and quantitative discussion of the inventory and mass balance of dissolved thallium (Tl) in the oceans. The calculations are based on a critical evaluation of recently published analytical data. Thallium is estimated to have a mean seawater concentration of 65 pmol/kg and this implies a total oceanic inventory of about 8.76×10 4 Mmol Tl. The five primary sources of dissolved Tl in the oceans are rivers, hydrothermal fluids, eolian contributions from volcanic emanations and mineral aerosols, and benthic fluxes from continental margin sediments. Combined, these sources generate a Tl flux of between 1.4 and 12 Mmol/year, with a best estimate of 5.2 Mmol/year. Based on this, an oceanic residence time of 7–63 ky is calculated for Tl, with a best estimate of 17 ky. The two main oceanic sinks of Tl are scavenging from seawater by the authigenic phases of pelagic clays and uptake of Tl during low-temperature alteration of oceanic crust. These sinks remove about 1.6–7.7 Mmol/year of Tl, with a best estimate of 4.2 Mmol/year. This indicates an oceanic residence time of 11–56 ky, with a best estimate of 21 ky. The mass balance yields input and output fluxes which are identical, within the uncertainties, and this is in accord with a budget that is in steady state.