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
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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…
Interannual rainfall variations in equatorial East Africa are tightly linked to the El Niño Southern Oscillation (ENSO), with more rain and flooding during El Niño and droughts in La Niña years, both having severe impacts on human habitation and food security. Here we report evidence from an annually laminated lake sediment record from…
Experiments with two well-studied denitrifiers and one recently isolated marine suboxic zone denitrifier show that the cellular-level denitrification N isotope effect ( 15ε) is typically lower than the canonical value of ∼25‰ under many conditions prevalent in the ocean. Across all three strains, 15ε is 10-15‰ at cellular nitrate reduction rates…
The 15N composition of sediments has been used as a proxy for nitrate utilization in surface waters to assess the role of Southern Ocean export production in glacial/interglacial changes in atmospheric CO2 concentration. Interpretation has relied on a temporally constant isotope effect (ε) associated with uptake and assimilation of nitrate by…
In environmental water samples that contain both nitrate (NO 3-) and nitrite (NO2-), isotopic analysis of nitrate alone by all currently available methods requires pretreatment to remove nitrite. Sulfamic acid addition, used previously for this purpose (Wu JP, Calvert SE, Wong CS. Deep-Sea Research Part I - Oceanographie Research Papers 1997; 44…
From 1.25 million to 700,000 years ago, the ice age cycle deepened and lengthened from 41,000- to 100,000-year periodicity, a transition that remains unexplained. Using surface- and bottom-dwelling foraminifera from the Antarctic Zone of the Southern Ocean to reconstruct the deep-to-surface supply of water during the ice ages of the past 1.5…
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…