Swart Peter K.

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Swart
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Peter K.
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Anomalous delta C-13 in particulate organic carbon at the chemoautotrophy maximum in the Cariaco Basin

2020-01-30 , Scranton, Mary I. , Taylor, Gordon T. , Thunell, Robert C. , Muller-Karger, Frank E. , Astor, Yrene , Swart, Peter K. , Edgcomb, Virginia P. , Pachiadaki, Maria G.

A chemoautotrophy maximum is present in many anoxic basins at the sulfidic layer's upper boundary, but the factors controlling this feature are poorly understood. In 13 of 31 cruises to the Cariaco Basin, particulate organic carbon (POC) was enriched in 13C (δ13CPOC as high as −16‰) within the oxic/sulfidic transition compared to photic zone values (−23 to −26‰). During “heavy” cruises, fluxes of O2 and [NO3− + NO2−] to the oxic/sulfidic interface were significantly lower than during “light” cruises. Cruises with isotopically heavy POC were more common between 2013 and 2015 when suspended particles below the photic zone tended to be nitrogen rich compared to later cruises. Within the chemoautotrophic layer, nitrogen‐rich particles (molar ratio C/N< 10) were more likely to be 13C‐enriched than nitrogen‐poor particles, implying that these inventories were dominated by living cells and fresh detritus rather than laterally transported or extensively decomposed detritus. During heavy cruises, 13C enrichments persisted to 1,300 m, providing the first evidence of downward transport of chemoautotrophically produced POC. Dissolved inorganic carbon assimilation during heavy cruises (n = 3) was faster and occurred deeper than during light cruises (n = 2). Metagenomics data from the chemoautotrophic layer during two cruises support prevalence of microorganisms carrying RuBisCO form II genes, which encode a carbon fixation enzyme that discriminates less against heavy isotopes than most other carbon fixation enzymes, and metatranscriptomics data indicate that higher expression of form II RuBisCO genes during the heavy cruises at depths where essential reactants coexist are responsible for the isotopically heavier POC.

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Salinity change in the subtropical Atlantic : secular increase and teleconnections to the North Atlantic Oscillation

2005-01-21 , Rosenheim, Brad E. , Swart, Peter K. , Thorrold, Simon R. , Eisenhauer, Anton , Willenz, Philippe

Recent studies comparing shipboard data between the 1950's and the 1990's have shown significant, heterogeneous adjustments of the temperature-salinity structure of the N. Atlantic Ocean. Here, we present proxy records of temperature and salinity from aragonite sclerosponge skeletons, extending existing records of the Salinity Maximum Waters (SMW) of the N. Atlantic back to 1890. These proxy records show secular temperature increases of 1.6–2.0°C, higher than published global averages, and salinity increases of 0.35–0.5 psu, smaller than short-term secular trends recently measured. Salinity reconstructions vary more significantly on the decadal scale, showing changes that are related to low-frequency variations of the North Atlantic Oscillation (NAO). On both secular and decadal time scales, the records indicate significant thermohaline changes in the SMW, either via forcing at the surface or increasing depths of density surfaces in the Bahamas.

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Evidence of multidecadal salinity variability in the eastern tropical North Atlantic

2006-08-17 , Moses, Christopher S. , Swart, Peter K. , Rosenheim, Brad E.

Ocean circulation and global climate are strongly influenced by seawater density, which is itself controlled by salinity and temperature. Although adequate instrumental sea-surface temperature (SST) records exist for most of the surface oceans over the past 100-150 years, records of salinity really only exist for the last 40-50 years. Here we show that longer proxy records from corals (Siderastrea radians) in the eastern tropical North Atlantic are dominated by multi-decadal variations in salinity which are correlated with the relationship between SST and the North Atlantic Oscillation (NAO) over the course of the 20th century. The data reveal an increase in eastern tropical North Atlantic salinity of +0.5 psu between about 1950-1990. Rather than a monotonic secular increase, as indicated by some instrumental records, the pre-instrumental coral proxy records presented here suggest that salinity in the tropical North Atlantic is periodic on a decadal to multi-decadal scale.

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