Studies in the Modern Ocean

CTD/hydrocast package descending into the Southern Ocean. Photo Kenemy

The CTD/hydrocast package descending into the Southern Ocean water column from the deck of the South African research icebreaker S.A. Agulhas II, sailing from Cape Town to the Antarctic winter ice edge. Photo: Preston Cosslett Kemeny ’15

 

References

16 Publications
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The original version of this Article contained errors in Fig. 2b and Table 2. In Fig. 2b, the white circle labels were incorrectly positioned as they referred to scenarios that were used in an earlier version of the Article. In Table 2, the following three sentences were removed from the legend The last two calculations are discussed in the …
Nitrate persists in eastern equatorial Pacific surface waters because phytoplankton growth fueled by nitrate (new production) is limited by iron. Nitrate isotope measurements provide a new constraint on the controls of surface nitrate concentration in this region and allow us to quantify the degree and temporal variability of nitrate consumption…
Equatorial Pacific nitrate 15N/14N and 18O/16O (δ15N and δ18O) measurements from repeat station occupations are used to: (1) identify the source of surface waters, (2) estimate the nitrate assimilation isotope effect, (3) characterize the temporal relationship between the supply and consumption of nitrate in surface waters, and (4) quantify the…
The difference between nitrate δ15N and δ18O, or Δ(15-18), is sensitive to organic matter remineralization and tracks the modification of nitrate as it passes from the deep Pacific Ocean, through the Southern Ocean surface, and into the intermediate-depth Pacific. Circumpolar Deep Water (CDW) is upwelled with a nitrate Δ(15-18) of +3.0‰ and…
We report measurements of the nitrogen isotopic composition of nitrate (the δ 15N of NO 3 -) across the equatorial Pacific, for zonal transects from 165E to 95W and meridional transects across 95 and 110W. The δ 15N of NO 3 - is similar in the equatorial thermocline (100 m) and intermediate depth waters (150 to 600 m), averaging (7.1 0.3)‰ and (7…
The continental shelves are the most biologically dynamic regions of the ocean, and they are extensive worldwide, especially in the western North Pacific. Their area has varied dramatically over the glacial/interglacial cycles of the last million years, but the effects of this variation on ocean biological and chemical processes remain poorly…
With the rapid rise in pollution-associated nitrogen inputs to the western Pacific, it has been suggested that even the open ocean has been affected. In a coral core from Dongsha Atoll, a remote coral reef ecosystem, we observe a decline in the 15N/14N of coral skeleton-bound organic matter, which signals increased deposition of anthropogenic…
Reduced nitrate supply to the subarctic North Pacific (SNP) surface during the last ice age has been inferred from coupled changes in diatom-bound δ15N (DB-δ15N), bulk sedimentary δ15N, and biogenic fluxes. However, the reliability of bulk sedimentary and DB-δ15N has been questioned, and a previously reported δ15N minimum during Heinrich Stadial 1…
The chemistry and isotopic composition of siliceous diatom frustules and the organic matter bound within them have been used to reconstruct past changes in the environment. However, the alteration of biogenic silica in the sediments and its influence on the chemical properties of the diatom opal and diatom-bound organic matter has not been broadly…
We report a new foraminifera-bound δ 15N (FB-δ 15N) record from the South China Sea (SCS) extending back to 42ka. This record shows a ∼1.2‰ glacial-to-interglacial δ 15N decrease, with a deglacial δ 15N maximum similar to that observed in many bulk sedimentary δ 15N records and in a Caribbean FB-δ 15N record. The glacial-to-interglacial δ 15N…
We investigated the controls on the δ15N values of shell-bound organic matter of planktonic foraminifera (foraminifera-bound δ15N, or FB-δ15N). The bulk biomass δ15N of live foraminifera collected from plankton tows at Sta. S in the Sargasso Sea is within ∼1‰ of the FB-δ15N of the same species picked from surface sediments from the low-latitude…
Fixed nitrogen (N) is a limiting nutrient for algae in the low-latitude ocean, and its oceanic inventory may have been higher during ice ages, thus helping to lower atmospheric CO2 during those intervals. In organic matter within planktonic foraminifera shells in Caribbean Sea sediments, we found that the 15N/14N ratio from the last ice age is…
Surface sediment diatom-bound δ15N along a latitudinal transect of 170°W shows a previously unobserved increase to the South of the Antarctic Polar Front. The southward δ15N increase is best explained by the combination of two changes toward the South, a decrease in the isotope effect of nitrate assimilation (ε) and an increase in the degree of…
Diatom-bound 15N/14N was used to reconstruct the glacial nutrient status of the Subantarctic Zone in the Southern Ocean. Down-core records from both the Pacific and Indian sectors show δ 15N of 5 to 6%‰ during the Last Glacial Maximum and a decrease, coincident with the glacial termination, to values as low as 2‰. The effect of either diatom…
Isotopic measurements of diatom-bound nitrogen, using a wet chemical oxidation combined with the "denitrifier" method for nitrate analysis, show significant offsets from previously published combustion-based measurements. This offset is attributed to a gaseous nitrogen blank associated with the diatom s opal frustule. Moreover, experimentation…
The stable nitrogen (N) and oxygen (O) isotope ratios (15N/14N and 18O/16O, respectively) of nitrate (NO3-) were measured during incubations of freshly collected seawater to investigate the effect of light intensity on the isotope fractionation associated with nitrate assimilation and possible co-occurring regeneration and nitrification by in situ…