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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A growing number of paleoceanographic observations suggest that the ocean s deep ventilation is stronger in warm climates than in cold climates. Here we use a general ocean circulation model to test the hypothesis that this relation is due to the reduced sensitivity of seawater density to temperature at low mean temperature; that is, at lower…
Most biological nitrogen transformations have characteristic kinetic isotope effects used to track these processes in modern and past environments. The isotopic fractionation associated with nitrogen fixation, the only biological source of fixed nitrogen (N), provides a particularly important constraint for studies of nitrogen cycling. Nitrogen…
Reconstructed changes in seawater calcium and magnesium concentration ([Ca2+], [Mg2+]) predictably affect the ocean s acid/base and carbon chemistry. Yet inaccurate formulations of chemical equilibrium "constants" are currently in use to account for these changes. Here we develop an efficient implementation of the MIAMI Ionic Interaction Model to…
We conducted a survey of the natural abundance 15N/14N ratio (δ15N) of particulate organic matter (POM), diatom frustule-bound nitrogen (δ15NDB), and zooplankton from water column material collected with net tows across the eastern Bering Sea shelf in late winter of 2007 and 2008, to investigate the N dynamics of primary and secondary production…
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…
The nitrogen isotopic composition (15N/14N ratio, or δ15N) of enameloid-bound organic matter (δ15NEB) in shark teeth was recently developed to investigate the biogeochemistry and trophic structures (i.e., food webs) of the ancient ocean. Using δ15NEB, we present the first nitrogen isotopic evidence for trophic differences between shark taxa from a…

Dissolved oxygen (O2) is essential for most ocean ecosystems, fuelling organisms’ respiration and facilitating the cycling of carbon and nutrients. Oxygen measurements have been interpreted to indicate that the ocean’s oxygen-deficient zones (ODZs) are expanding under global warming1,2. However, models provide an unclear picture of future ODZ…

Coincident with the intensification of Northern Hemisphere Glaciation (NHG) around 2.73 million years (Ma) ago, sediment cores from both the open subarctic North Pacific and the Antarctic indicate a rapid decline in diatom opal accumulation flux to the seabed, representing one of the most abrupt and dramatic changes in the marine sediment record…
In the Southern Ocean, the nitrogen (N) isotopes of organic matter and the N and oxygen (O) isotopes of nitrate (NO3 −) have been used to investigate NO3 − assimilation and N cycling in the summertime period of phytoplankton growth, both today and in the past. However, recent studies indicate the significance of processes in other seasons for…
(Figure Presented) Figure 4. Cycle of biologically driven N transformations that occur in natural and human-influenced terrestrial and marine environments. Nitrogen (N2) fixation (step 1) and N assimilation (from ammonium, nitrate, or organic N, step 2) are anabolic processes, whereas mineralization (step 3), nitrification (steps 4−6), DNRA (steps 7,…
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 …
In order to (i) establish the biological systematics necessary to interpret nitrogen (N) and oxygen (O) isotope ratios of nitrate (15N/ 14N and 18O/16O) in the environment and (ii) investigate the potential for isotopes to elucidate the mechanism of a key N cycle enzyme, we measured the nitrate N and O isotope effects ( 15ε and 18ε) for nitrate…
Using an ocean box model, we have studied the effect of altered circulation on the oceanic distributions of phosphate (PO4-3) and the 13C/12C and 14C/12C of dissolved inorganic carbon to evaluate competing hypotheses for the cause of observed nutrient depletion and 13C enrichment at intermediate depths of the Atlantic during the last ice age…
In a piston core from the central Bering Sea, diatom microfossil-bound N isotopes and the concentrations of Opal, biogenic barium, calcium carbonate, and organic N are measured over the last glacial/interglacial cycle. Compared to the interglacial sections of the core, the sediments of the last ice age are characterized by 3‰ higher diatom-bound…