Hendry Katharine R.

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Hendry

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Katharine R.

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0000-0002-0790-5895

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Silicon isotopes in Antarctic sponges : an interlaboratory comparison

( 2010-06-08) Hendry, Katharine R. ; Leng, Melanie J. ; Robinson, Laura F. ; Sloane, Hilary J. ; Blusztajn, Jerzy S. ; Rickaby, Rosalind E. M. ; Georg, R. Bastian ; Halliday, Alex N.

Cycling of deep-water silicon (Si) within the Southern Ocean, and its transport into other ocean basins, may be an important player in the uptake of atmospheric carbon, and global climate. Recent work has shown that the Si isotope (denoted by δ29Si or δ30Si) composition of deep-sea sponges reflects the availability of dissolved Si during growth, and is a potential proxy for past deep and intermediate water silicic acid concentrations. As with any geochemical tool, it is essential to ensure analytical precision and accuracy, and consistency between methodologies and laboratories. Analytical bias may exist between laboratories, and sponge material may have matrix effects leading to offsets between samples and standards. Here, we report an interlaboratory evaluation of Si isotopes in Antarctic and subAntarctic sponges. We review independent methods for measuring Si isotopes in sponge spicules. Our results show that separate subsamples of non-homogenised sponges measured by three methods yield isotopic values within analytical error for over 80% of specimens. The relationship between δ29Si and δ30Si in sponges is consistent with kinetic fractionation during biomineralisation. Sponge Si isotope analyses show potential as palaeoceaongraphic archives, and we suggest Southern Ocean sponge material would form a useful additional reference standard for future spicule analyses.
Delivering sustained, coordinated, and integrated observations of the Southern Ocean for global impact

(Frontiers Media, 2019-08-08) Newman, Louise ; Heil, Petra ; Trebilco, Rowan ; Katsumata, Katsuro ; Constable, Andrew ; van Wijk, Esmee ; Assmann, Karen ; Beja, Joana ; Bricher, Phillippa ; Coleman, Richard ; Costa, Daniel P. ; Diggs, Stephen ; Farneti, Riccardo ; Fawcett, Sarah E. ; Gille, Sarah T. ; Hendry, Katharine R. ; Henley, Sian ; Hofmann, Eileen E. ; Maksym, Ted ; Mazloff, Matthew R. ; Meijers, Andrew J. S. ; Meredith, Michael M. ; Moreau, Sebastien ; Ozsoy, Burcu ; Robertson, Robin ; Schloss, Irene ; Schofield, Oscar M. E. ; Shi, Jiuxin ; Sikes, Elisabeth L. ; Smith, Inga J. ; Swart, Sebastiaan ; Wahlin, Anna ; Williams, Guy ; Williams, Michael J. M. ; Herraiz-Borreguero, Laura ; Kern, Stefan ; Lieser, Jan ; Massom, Robert A. ; Melbourne-Thomas, Jessica ; Miloslavich, Patricia ; Spreen, Gunnar

The Southern Ocean is disproportionately important in its effect on the Earth system, impacting climatic, biogeochemical, and ecological systems, which makes recent observed changes to this system cause for global concern. The enhanced understanding and improvements in predictive skill needed for understanding and projecting future states of the Southern Ocean require sustained observations. Over the last decade, the Southern Ocean Observing System (SOOS) has established networks for enhancing regional coordination and research community groups to advance development of observing system capabilities. These networks support delivery of the SOOS 20-year vision, which is to develop a circumpolar system that ensures time series of key variables, and delivers the greatest impact from data to all key end-users. Although the Southern Ocean remains one of the least-observed ocean regions, enhanced international coordination and advances in autonomous platforms have resulted in progress toward sustained observations of this region. Since 2009, the Southern Ocean community has deployed over 5700 observational platforms south of 40°S. Large-scale, multi-year or sustained, multidisciplinary efforts have been supported and are now delivering observations of essential variables at space and time scales that enable assessment of changes being observed in Southern Ocean systems. The improved observational coverage, however, is predominantly for the open ocean, encompasses the summer, consists of primarily physical oceanographic variables, and covers surface to 2000 m. Significant gaps remain in observations of the ice-impacted ocean, the sea ice, depths >2000 m, the air-ocean-ice interface, biogeochemical and biological variables, and for seasons other than summer. Addressing these data gaps in a sustained way requires parallel advances in coordination networks, cyberinfrastructure and data management tools, observational platform and sensor technology, two-way platform interrogation and data-transmission technologies, modeling frameworks, intercalibration experiments, and development of internationally agreed sampling standards and requirements of key variables. This paper presents a community statement on the major scientific and observational progress of the last decade, and importantly, an assessment of key priorities for the coming decade, toward achieving the SOOS vision and delivering essential data to all end-users.
Evidence of silicic acid leakage to the tropical Atlantic via Antarctic Intermediate Water during Marine Isotope Stage 4

(John Wiley & Sons, 2013-06-27) Griffiths, James D. ; Barker, Stephen ; Hendry, Katharine R. ; Thornalley, David J. R. ; van de Flierdt, Tina ; Hall, Ian R. ; Anderson, Robert F.

Antarctic Intermediate Water (AAIW) and Subantarctic Mode Water (SAMW) are the main conduits for the supply of dissolved silicon (silicic acid) from the deep Southern Ocean (SO) to the low-latitude surface ocean and therefore have an important control on low-latitude diatom productivity. Enhanced supply of silicic acid by AAIW (and SAMW) during glacial periods may have enabled tropical diatoms to outcompete carbonate-producing phytoplankton, decreasing the relative export of inorganic to organic carbon to the deep ocean and lowering atmospheric pCO2. This mechanism is known as the “silicic acid leakage hypothesis” (SALH). Here we present records of neodymium and silicon isotopes from the western tropical Atlantic that provide the first direct evidence of increased silicic acid leakage from the Southern Ocean to the tropical Atlantic within AAIW during glacial Marine Isotope Stage 4 (~60–70 ka). This leakage was approximately coeval with enhanced diatom export in the NW Atlantic and across the eastern equatorial Atlantic and provides support for the SALH as a contributor to CO2 drawdown during full glacial development.
Erratum to “Deep ocean nutrients during the Last Glacial Maximum deduced from sponge silicon isotopic compositions” [Earth Planet. Sci. Lett. 292 (2010) 290–300]

( 2010-12) Hendry, Katharine R. ; Georg, R. Bastian ; Rickaby, Rosalind E. M. ; Robinson, Laura F. ; Halliday, Alex N.

The relative importance of biological and physical processes within the Southern Ocean for the storage of carbon and atmospheric pCO2 on glacial-interglacial timescales remains uncertain. Understanding the impact of surface biological production on carbon export in the past relies on the reconstruction of the nutrient supply from upwelling deep-waters. In particular, the upwelling of silicic acid (Si(OH)4) is tightly coupled to carbon export in the Southern Ocean via diatom productivity. Here, we address how changes in deep-water Si(OH)4 concentrations can be reconstructed using the silicon isotopic composition of deep-sea sponges. We report δ30Si of modern deep-sea sponge spicules and show that they reflect seawater Si(OH)4 concentration. The fractionation factor of sponge δ30Si compared to seawater δ30Si shows a positive relationship with Si(OH)4, which may be a growth rate effect. Application of this proxy in two down-core records from the Scotia Sea reveals that Si(OH)4 concentrations in the deep Southern Ocean during the Last Glacial Maximum (LGM) were no different than today. Our result does not support a coupling of carbon and nutrient build up in an isolated deep-ocean reservoir during the LGM. Our data, combined with records of stable isotopes from diatoms, are only consistent with enhanced LGM Southern Ocean nutrient utilization if there was also a concurrent reduction in diatom silicification or a shift from siliceous to organic-walled phytoplankton.
Changes in micronutrient supply to the surface Southern Ocean (Atlantic sector) across the glacial termination

(American Geophysical Union, 2011-09-16) Hendry, Katharine R. ; Rickaby, Rosalind E. M. ; Allen, Claire S.

Major deepwater masses upwell and reach the surface in the Southern Ocean, forming an important conduit supplying nutrients and micronutrients to the surface and playing a key role in the regulation of global climate through ocean-atmosphere gas exchange. Here, we reconstruct changes in micronutrient distribution in this region in response to past changes in upwelling, oceanic mixing, and sea-ice seasonality. We present two downcore (Zn/Si)opal records from the Scotia Sea and Drake Passage region, which we interpret in the context of micronutrient distribution in the Atlantic sector of the Southern Ocean over the last glacial termination. Previous work shows that micronutrient availability in the surface waters in the South Atlantic appear to be controlled dominantly by upwelling and mixing of micronutrient rich deepwaters, which are additionally fuelled by the terrestrial sediment sources of the Scotia Arc and South Georgia. This is supported by our reconstructions, which show micronutrient availability to the west of the Scotia Arc and South Georgia are consistently lower than to the east over the last glacial termination due to downstream transport and mixing into surface waters of continentally derived material in the Antarctic Circumpolar Current. Micronutrient availability in this region was at a minimum from 20 to 25 ky BP, coinciding with maximum sea-ice coverage, and increased due to an expansion of the seasonal sea-ice zone and increased mixing of subsurface waters. Our findings are consistent with largely diminished upwelling of micronutrients during the maximum glacial extent, and reduced mixing due to the presence of persistent sea-ice. During the deglacial there was an increase in micronutrient availability, as well as other nutrients and inorganic carbon, within the Antarctic Circumpolar Current as a result of an increase in deep oceanic upwelling, mixing and strengthened zonal transport.
Large subglacial source of mercury from the southwestern margin of the Greenland Ice Sheet

(Nature Research, 2021-05-24) Hawkings, Jon ; Linhoff, Benjamin S. ; Wadham, Jemma L. ; Stibal, Marek ; Lamborg, Carl H. ; Carling, Gregory T. ; Lamarche-Gagnon, Guillaume ; Kohler, Tyler J. ; Ward, Rachael ; Hendry, Katharine R. ; Falteisek, Lukáš ; Kellerman, Anne M. ; Cameron, Karen A. ; Hatton, Jade E. ; Tingey, Sarah ; Holt, Amy D. ; Vinšová, Petra ; Hofer, Stefan ; Bulínová, Marie ; Větrovský, Tomáš ; Meire, Lorenz ; Spencer, Robert G. M.

The Greenland Ice Sheet is currently not accounted for in Arctic mercury budgets, despite large and increasing annual runoff to the ocean and the socio-economic concerns of high mercury levels in Arctic organisms. Here we present concentrations of mercury in meltwaters from three glacial catchments on the southwestern margin of the Greenland Ice Sheet and evaluate the export of mercury to downstream fjords based on samples collected during summer ablation seasons. We show that concentrations of dissolved mercury are among the highest recorded in natural waters and mercury yields from these glacial catchments (521–3,300 mmol km−2 year−1) are two orders of magnitude higher than from Arctic rivers (4–20 mmol km−2 year−1). Fluxes of dissolved mercury from the southwestern region of Greenland are estimated to be globally significant (15.4–212 kmol year−1), accounting for about 10% of the estimated global riverine flux, and include export of bioaccumulating methylmercury (0.31–1.97 kmol year−1). High dissolved mercury concentrations (~20 pM inorganic mercury and ~2 pM methylmercury) were found to persist across salinity gradients of fjords. Mean particulate mercury concentrations were among the highest recorded in the literature (~51,000 pM), and dissolved mercury concentrations in runoff exceed reported surface snow and ice values. These results suggest a geological source of mercury at the ice sheet bed. The high concentrations of mercury and its large export to the downstream fjords have important implications for Arctic ecosystems, highlighting an urgent need to better understand mercury dynamics in ice sheet runoff under global warming.
Barium isotopes reveal role of ocean circulation on barium cycling in the Atlantic

( 2017-02-02) Bates, Stephanie L. ; Hendry, Katharine R. ; Pryer, Helena V. ; Kinsley, Christopher W. ; Pyle, Kimberley M. ; Woodward, E. Malcolm S. ; Horner, Tristan J.

We diagnose the relative influences of local-scale biogeochemical cycling and regional-scale ocean circulation on Atlantic barium cycling by analyzing four new depth profiles of dissolved Ba concentrations and isotope compositions from the South and tropical North Atlantic. These new profiles exhibit systematic vertical, zonal, and meridional variations that reflect the influence of both local-scale barite cycling and large-scale ocean circulation. Previously reported epipelagic decoupling of Ba and Si in the tropics is also found to be associated with significant Ba isotope heterogeneity. We contend that this decoupling originates from the depth segregation of opal & barite formation but is exacerbated by weak vertical mixing, as in the tropics. Zonal influence from isotopically-‘heavy’ water masses in the western North Atlantic evidence the advective inflow of Ba-depleted Upper Labrador Sea Water, which is not seen in the eastern basin or the South Atlantic. Meridional variations in Atlantic Ba isotope systematics below 2,000 m appear entirely controlled by conservative mixing. Using an inverse isotopic mixing model, we calculate the Ba isotope composition of the Ba-poor northern end member as +0.45 ‰ and the Ba-rich southern end member +0.26 ‰, relative to NIST SRM 3104a. The near-conservative behaviour of Ba in the deep ocean indicates that Ba isotopes may serve as an independent tracer of the provenance of advected water masses in the Atlantic Ocean. The clearly resolved Ba-isotope signatures of northern- and southern-sourced waters may also prove useful in paleoceanographic studies, should appropriate sedimentary archives be identified. Overall, our results offer new insights into the controls on Ba cycling in seawater and thus the mechanisms that underpin the utility of Ba-based proxies in paleoceanography.
The role of sea ice formation in cycling of aluminium in northern Marguerite Bay, Antarctica

( 2009-11-17) Hendry, Katharine R. ; Meredith, Michael P. ; Measures, Christopher I. ; Carson, Damien S. ; Rickaby, Rosalind E. M.

The use of dissolved Al as a tracer for oceanic water masses and atmospheric dust deposition of biologically important elements, such as iron, requires the quantitative assessment of its sources and sinks in seawater. Here, we address the relative importance of oceanic versus atmospheric inputs of Al, and the relationship with nutrient cycling, in a region of high biological productivity in coastal Antarctica. We investigate the concentrations of dissolved Al in seawater, sea ice, meteoric water and sediments collected from northern Marguerite Bay, off the West Antarctic Peninsula, from 2005-2006. Dissolved Al concentrations at 15 m water depth varied between 2 and 27 nM, showing a peak between two phytoplankton blooms. We find that, in this coastal setting, upwelling and incorporation of waters from below the surface mixed layer are responsible for this peak in dissolved Al as well as renewal of nutrients. This means that changes in the intensity and frequency of upwelling events may result in changes in biological production and carbon uptake. The waters below the mixed layer are most likely enriched in Al as a result of sea ice formation, either causing the injection of Al-rich brines or the resuspension of sediments and entrainment of pore fluids by brine cascades. Glacial, snow and sea ice melt contributes secondarily to the supply of Al to surface waters. Total particulate Al ranges from 93 to 2057 μg/g, and increases with meteoric water input towards the end of the summer, indicating glacial runoff is an important source of particulate Al. The (Al/Si)opal of sediment core top material is considerably higher than water column opal collected by sediment traps, indicative of a diagenetic overprint and incorporation of Al at the sediment-water interface. Opal that remains buried in the sediment could represent a significant sink of Al from seawater.
Controls on stable isotope and trace metal uptake in Neogloboquadrina pachyderma (sinistral) from an Antarctic sea-ice environment

( 2008-11) Hendry, Katharine R. ; Rickaby, Rosalind E. M. ; Meredith, Michael P. ; Elderfield, Henry

The polar foraminifera Neogloboquadrina pachyderma (sinistral) dominates assemblages from the high latitude Southern Ocean, which is a key region for paleoclimate studies. Here, we use N. pachyderma (s.) harvested from sediment traps off the West Antarctic Peninsula to construct a seasonal time series for the calibration of calcite proxies in a high latitude seasonal sea-ice environment where temperature is decoupled from other environmental parameters. We have used a combination of δ18OCaCO3 and δ13CCaCO3 to decipher the calcification temperature and salinity, which reflect that N. pachyderma (s.) live in surface waters throughout the year, and at the ice-water interface in austral winter. Further, our results demonstrate that, during winter, the uptake of trace metals into N. pachyderma (s.) calcite is influenced by secondary environmental conditions in addition to temperature during periods of sea-ice. We suggest an elevated carbonate ion concentration at the ice-water interface resulting from biological utilisation CO2 could influence calcification in foraminifera. We demonstrate that for N. pachyderma (s.) Mg/Ca and Sr/Ca ratios are linear functions of calcification temperature and [CO32-]. N. pachyderma (s.) Mg/Ca ratios exhibit temperature sensitivity similar to previous studies (~ 10 % per °C) and a sensitivity to [CO32-] of ~ 1 % per μmol kg-1). Sr/Ca ratios are less sensitive to environmental parameters, exhibiting < 1% increase per °C and per 10 μmol kg-1. We show how a multi-proxy approach could be used to constrain past high latitude surface water temperature and [CO32-].
Opal (Zn/Si) ratios as a nearshore geochemical proxy in coastal Antarctica

(American Geophysical Union, 2008-06-18) Hendry, Katharine R. ; Rickaby, Rosalind E. M.

During the last 50 years, the Antarctic Peninsula has experienced rapid warming with associated retreat of 87% of marine and tidewater glacier fronts. Accelerated glacial retreat and iceberg calving may have a significant impact on the freshwater and nutrient supply to the phytoplankton communities of the highly productive coastal regions. However, commonly used biogenic carbonate proxies for nutrient and salinity conditions are not preserved in sediments from coastal Antarctica. Here we describe a method for the measurement of zinc to silicon ratios in diatom opal, (Zn/Si)opal, which is a potential archive in Antarctic marine sediments. A core top calibration from the West Antarctic Peninsula shows (Zn/Si)opal is a proxy for mixed layer salinity. We present down-core (Zn/Si)opal paleosalinity records from two rapidly accumulating sites taken from nearshore environments off the West Antarctic Peninsula which show an increase in meltwater input in recent decades. Our records show that the recent melting in this region is unprecedented for over 120 years.
Cadmium and phosphate in coastal Antarctic seawater : implications for Southern Ocean nutrient cycling

( 2008-09) Hendry, Katharine R. ; Rickaby, Rosalind E. M. ; de Hoog, Jan C. M. ; Weston, Keith ; Rehkamper, Mark

Cadmium is a biologically important trace metal that co-varies with phosphate (PO43- or Dissolved Inorganic Phosphate, DIP) in seawater. However, the exact nature of Cd uptake mechanisms and the relationship with phosphate and other nutrients in global oceans remains elusive. Here, we present a time series study of Cd and PO43- from coastal Antarctic seawater, showing that Cd co-varies with macronutrients during times of high biological activity even under nutrient and trace metal replete conditions. Our data imply that Cd/PO43- in coastal surface Antarctic seawater is higher than open ocean areas. Furthermore, the sinking of some proportion of this high Cd/PO43- water into Antarctic Bottom Water, followed by mixing into Circumpolar Deep Water, impacts Southern Ocean preformed nutrient and trace metal composition. A simple model of endmember water mass mixing with a particle fractionation of Cd/P (αCd-P) determined by the local environment can be used to account for the Cd/PO43- relationship in different parts of the ocean. The high Cd/PO43- of the coastal water is a consequence of two factors: the high input from terrestrial and continental shelf sediments and changes in biological fractionation with respect to P during uptake of Cd in regions of high Fe and Zn. This implies that the Cd/PO43- ratio of the Southern Ocean will vary on glacial-interglacial timescales as the proportion of deep water originating on the continental shelves of the Weddell Sea is reduced during glaciations because the ice shelf is pinned at the edge of the continental shelf. There could also be variations in biological fractionation of Cd/P in the surface waters of the Southern Ocean on these timescales as a result of changes in atmospheric inputs of trace metals. Further variations in the relationship between Cd and PO43- in seawater arise from changes in population structure and community requirements for macro- and micronutrients.
Deep ocean nutrients during the Last Glacial Maximum deduced from sponge silicon isotopic compositions

( 2010-02) Hendry, Katharine R. ; Georg, R. Bastian ; Rickaby, Rosalind E. M. ; Robinson, Laura F. ; Halliday, Alex N.

The relative importance of biological and physical processes within the Southern Ocean for the storage of carbon and atmospheric pCO2 on glacial-interglacial timescales remains uncertain. Understanding the impact of surface biological production on carbon export in the past relies on the reconstruction of the nutrient supply from upwelling deep-waters. In particular, the upwelling of silicic acid (Si(OH)4) is tightly coupled to carbon export in the Southern Ocean via diatom productivity. Here, we address how changes in deep-water Si(OH)4 concentrations can be reconstructed using the silicon isotopic composition of deep-sea sponges. We report δ30Si of modern deep-sea sponge spicules and show that they reflect seawater Si(OH)4 concentration. The fractionation factor of sponge δ30Si compared to seawater δ30Si shows a positive relationship with Si(OH)4, which may be a growth rate effect. Application of this proxy in two down-core records from the Scotia Sea reveals that Si(OH)4 concentrations in the deep Southern Ocean during the Last Glacial Maximum (LGM) were no different than today. Our result does not support a coupling of carbon and nutrient build up in an isolated deep-ocean reservoir during the LGM. Our data, combined with records of stable isotopes from diatoms, are only consistent with enhanced LGM Southern Ocean nutrient utilization if there was also a concur rent reduction in diatom silicification or a shift from siliceous to organic walled phytoplankton.
Silicon isotopes indicate enhanced carbon export efficiency in the North Atlantic during deglaciation

( 2013-11-11) Hendry, Katharine R. ; Robinson, Laura F. ; McManus, Jerry F. ; Hays, James D.

Today's Sargasso Sea is nutrient-starved, except for episodic upwelling events caused by wind-driven winter mixing and eddies. Enhanced diatom opal burial in Sargasso Sea sediments indicates that silicic acid, a limiting nutrient today, may have been more available in subsurface waters during Heinrich Stadials, the millennial-scale climate perturbations of the last glacial and deglaciation. Here we use the geochemistry of opalforming organisms from different water depths to demonstrate changes in silicic acid supply and utilisation during the most recent Heinrich Stadial. We suggest that during the early phase (17.5-18 ka), wind-driven upwelling replenished silicic acid to the subsurface, resulting in low Si utilisation. By 17ka, stratification reduced the surface silicic acid supply and increased Si utilization efficiency. This abrupt shift in Si cycling would have contributed to high regional carbon export efficiency during the recent Heinrich Stadial, despite being a period of increasing atmospheric CO2.
Diatom silicon isotopes as a proxy for silicic acid utilisation : a Southern Ocean core top calibration

(Elsevier, 2012-08-11) Egan, Katherine E. ; Rickaby, Rosalind E. M. ; Leng, Melanie J. ; Hendry, Katharine R. ; Hermoso, Michael ; Sloane, Hilary J. ; Bostock, Helen ; Halliday, Alex N.

Despite a growing body of work that uses diatom δ30Si to reconstruct past changes in silicic acid utilisation, few studies have focused on calibrating core top data with modern oceanographic conditions. In this study, a microfiltration technique is used to divide Southern Ocean core top silica into narrow size ranges, separating components such as radiolaria, sponge spicules and clay minerals from diatoms. Silicon isotope analysis of these components demonstrates that inclusion of small amounts of non-diatom material can significantly offset the measured from the true diatom δ30Si. Once the correct size fraction is selected (generally 2–20 μm), diatom δ30Si shows a strong negative correlation with surface water silicic acid concentration (R2 = 0.92), highly supportive of the qualitative use of diatom δ30Si as a proxy for silicic acid utilisation. The core top diatom δ30Si matches well with mixed layer filtered diatom δ30Si from published in situ studies, suggesting little to no effect of either dissolution on export through the water column, or early diagenesis, on diatom δ30Si in sediments from the Southern Ocean. However, the core top diatom δ30Si shows a poor fit to simple Rayleigh or steady state models of the Southern Ocean when a single source term is used. The data can instead be described by these models only when variations in the initial conditions of upwelled silicic acid concentration and δ30Si are taken into account, a caveat which may introduce some error into quantitative reconstructions of past silicic acid utilisation from diatom δ30Si.
The relationship between silicon isotope fractionation in sponges and silicic acid concentration : modern and core-top studies of biogenic opal

( 2011-11-14) Hendry, Katharine R. ; Robinson, Laura F.

Recent work has shown the silicon isotope composition, denoted by δ30Si, of deep-sea sponges reflects the concentration of ambient silicic acid (Si(OH)4) in seawater. However, existing calibrations are based predominantly on living sponges collected from the Southern Ocean. These data cannot, however, be used to determine whether other parameters that correlate with silicic acid in the Southern Ocean, such as temperature and salinity, influence δ30Si of sponges. Furthermore, the published data do not demonstrate whether disaggregated core-top sedimentary spicules preserve the primary δ30Si signal recorded in living sponges. Here, we address both of these issues. We refine and widen the existing calibration by including a global distribution of modern sponges. In addition, we provide the first systematic calibration from spicules picked from core-top sediments that covers sites from different ocean basins. The relationship between Si(OH)4 and δ30Si in sponge spicules is the same in different ocean basins, between specimens that grew in different temperature and salinity conditions. Our core-top data agree well with the modern sponge calibration indicating there are no significant post-depositional effects or early diagenetic overprints. These two new datasets support the assertion that sponge δ30Si can be used as a proxy for silicic acid concentrations in the past.
Clumped isotope composition of cold-water corals : a role for vital effects?

(Elsevier, 2016-02-02) Spooner, Peter T. ; Guo, Weifu ; Robinson, Laura F. ; Thiagarajan, Nivedita ; Hendry, Katharine R. ; Rosenheim, Brad E. ; Leng, Melanie J.

The carbonate clumped isotope thermometer is a promising tool for determining past ocean temperatures. It is based on the temperature dependence of rare isotopes ‘clumping’ into the same carbonate ion group in the carbonate mineral lattice. The extent of this clumping effect is independent of the isotope composition of the water from which carbonate precipitates, providing unique advantages over many other paleotemperature proxies. Existing calibrations of this thermometer in cold-water and warm-water corals suggest clumped isotope ‘vital effects’ are negligible in cold-water corals but may be significant in warm-water corals. Here, we test the calibration of the carbonate clumped isotope thermometer in cold-water corals with a recently collected and well characterised sample set spanning a range of coral genera (Balanophyllia, Caryophyllia, Dasmosmilia, Desmophyllum, Enallopsammia and Javania). The clumped isotope compositions (Δ47) of these corals exhibit systematic dependences on their growth temperatures, confirming the basis of the carbonate clumped isotope thermometer. However, some cold-water coral genera show Δ47 values that are higher than the expected equilibrium values by up to 0.05‰ (equivalent to underestimating temperature by ∼9 °C) similar to previous findings for some warm-water corals. This finding suggests that the vital effects affecting corals Δ47 are common to both warm- and cold-water corals. By comparison with models of the coral calcification process we suggest that the clumped isotope offsets in these genera are related to the kinetic isotope effects associated with CO2 hydration/hydroxylation reactions in the corals’ calcifying fluid. Our findings complicate the use of the carbonate clumped isotope thermometer in corals, but suggest that species- or genus-specific calibrations could be useful for the future application of this paleotemperature proxy.

Hendry Katharine R.

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