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

AuthorTitleTypeYear
24 Publications
Applied Filters: First Letter Of Title: I Reset
Ice Age-Holocene Similarity of Foraminifera-Bound Nitrogen Isotope Ratios in the Eastern Equatorial Pacific
A.S. Studer, F. Mekik, H.A. Ren, M.P. Hain, S. Oleynik, A. Martínez-García, G.H. Haug, D.M. Sigman
Bulk sediment δ15N records from the eastern tropical Pacific (ETP) extending back to the last ice age most often show low glacial δ15N, then a deglacial δ15N maximum, followed by a gradual decline to a late Holocene δ15N that is typically higher than that of the Last Glacial Maximum (LGM). The lower δ15N of the LGM has been interpreted to reflect…
Impact of glacial/interglacial sea level change on the ocean nitrogen cycle
H.A. Ren, D.M. Sigman, A. Martínez-García, R.F. Anderson, M.-T. Chen, A.C. Ravelo, M. Straub, G.T.F. Wong, G.H. Haug
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…
The Impact of Incomplete Nutrient Consumption in the Southern Ocean on Global Mean Ocean Nitrate δ15N
F. Fripiat, D.M. Sigman, A. Martínez-García, D. Marconi, X.E. Ai, A. Auderset, S.E. Fawcett, S. Moretti, A.S. Studer, G.H. Haug

It is understood that the global mean ocean nitrate δ15N is set by the δ15N of the input of fixed nitrogen (N) to the ocean (mostly N2 fixation) and the net isotopic discrimination of fixed N loss (mostly denitrification). Here, we demonstrate that, in addition to the fixed nitrogen input/output budget, the isotopic discrimination of nitrate…

In-line optical subtraction using a differential Faraday rotation spectrometer for 15NO/14NO isotopic analysis
E. Zhang, D.M. Sigman, Gerard Wysocki

We present a dual-modulation Faraday rotation spectrometer with in-line optical subtraction for differential measurement of nitric oxide (NO) isotopologues. In-situ sample referencing is accomplished via differential dual-cell measurements, with 3.1 ppbv/rt(Hz) (15NO) sensitivity through 15 cm optical path length. Our system operates at 1.9x…

Increased nutrient supply to the Southern Ocean during the Holocene and its implications for the pre-industrial atmospheric CO2 rise
A.S. Studer, D.M. Sigman, A. Martínez-García, L.M. Thöle, E. Michel, S.L. Jaccard, J.A. Lippold, A. Mazaud, X.T. Wang, L.F. Robinson, J.F. Adkins, G.H. Haug
A rise in the atmospheric CO2 concentration of 20 parts per million over the course of the Holocene has long been recognized as exceptional among interglacials and is in need of explanation. Previous hypotheses involved natural or anthropogenic changes in terrestrial biomass, carbonate compensation in response to deglacial outgassing of oceanic…
Influence of ocean heat transport on the climate of the Last Glacial Maximum
R.S. Webb, D.H. Rind, S.J. Lehman, R.J. Healy, D.M. Sigman
A aeries of climate simulations using on atmospheric general circulation modal shows that maintaining ocean heat transport at close to present-day values, but with otherwise glacial boundary conditions, leads to an enhanced cooling, particularly in the tropics. This is in agreement with recent geochemical evidence from fossil corals, ground waters…
Influence of open ocean nitrogen supply on the skeletal δ15N of modern shallow-water scleractinian corals
X.T. Wang, D.M. Sigman, A.L. Cohen, D.J. Sinclair, R.M. Sherrell, K.M. Cobb, D.V. Erler, J. Stolarski, M.V. Kitahara, H.A. Ren
The isotopic composition of skeleton-bound organic nitrogen in shallow-water scleractinian corals (hereafter, CS-δ15N) is an emerging tool for studying the marine nitrogen cycle in the past. The CS-δ15N has been shown to reflect the δ15N of nitrogen (N) sources to corals, with most applications to date focusing on the anthropogenic/terrestrial N…
Influence of the intertropical convergence zone on the East Asian monsoon
G. Yancheva, N.R. Nowaczyk, J. Mingram, P. Dulski, G. Schettler, J.F.W. Negendank, J. Liu, D.M. Sigman, L.C. Peterson, G.H. Haug

The Asian-Australian monsoon is an important component of the Earth s climate system that influences the societal and economic activity of roughly half the world s population. The past strength of the rain-bearing East Asian summer monsoon can be reconstructed with archives such as cave deposits, but the winter monsoon has no such signature in…

Insights into anthropogenic nitrogen deposition to the North Atlantic investigated using the isotopic composition of aerosol and rainwater nitrate
A.R. Gobel, K.E. Altieri, A.J. Peters, M.G. Hastings, D.M. Sigman
Identifying the dominant sources of atmospheric reactive nitrogen (N r) is critical for determining the influence of anthropogenic emissions on Nr deposition, especially in marine ecosystems. To test the influence of anthropogenic versus marine air masses, samples were collected in Bermuda, where seasonal atmospheric circulation patterns lead to…
Instabilities Across the Agulhas Current Enhance Upward Nitrate Supply in the Southwest Subtropical Indian Ocean
T.A. Marshall, L.M. Beal, D.M. Sigman, S.E. Fawcett
The Agulhas Current, like other western boundary currents (WBCs), transports nutrients laterally from the tropics to the subtropics in a subsurface “nutrient stream.” These nutrients are predominantly supplied to surface waters by seasonal convective mixing, to fuel a brief period of productivity before phytoplankton become nutrient-limited…
Interbasin isotopic correspondence between upper-ocean bulk DON and subsurface nitrate and its implications for marine nitrogen cycling
A.N. Knapp, D.M. Sigman, F. Lipschultz, A.B. Kustka, D.G. Capone
Measurements to date have shown that both bulk and high molecular weight marine dissolved organic nitrogen (DON) have a 15N/ 14N that is substantially higher than the 15N/ 14N of suspended particulate organic nitrogen (PN susp) found in the same surface waters (with δ 15N of ∼4 to 5‰ and ∼-1 to 1‰, respectively). Moreover, the concentration and…
Iron fertilization of the subantarctic ocean during the last ice age
A. Martínez-García, D.M. Sigman, H.A. Ren, R.F. Anderson, M. Straub, D.A. Hodell, S.L. Jaccard, T.I. Eglinton, G.H. Haug
John H. Martin, who discovered widespread iron limitation of ocean productivity, proposed that dust-borne iron fertilization of Southern Ocean phytoplankton caused the ice age reduction in atmospheric carbon dioxide (CO2). In a sediment core from the Subantarctic Atlantic, we measured foraminifera-bound nitrogen isotopes to reconstruct ice age…
The isotope effect of nitrate assimilation in the Antarctic Zone: Improved estimates and paleoceanographic implications
F. Fripiat, A. Martínez-García, S.E. Fawcett, P.C. Kemeny, A.S. Studer, S.M. Smart, F. Rubach, S. Oleynik, D.M. Sigman, G.H. Haug
Both the nitrogen (N) isotopic composition (δ 15 N) of the nitrate source and the magnitude of isotope discrimination associated with nitrate assimilation are required to estimate the degree of past nitrate consumption from the δ 15 N of organic matter in Southern Ocean sediments (e.g., preserved within diatom microfossils). It has been suggested…
Isotopic composition of carbonate-bound organic nitrogen in deep-sea scleractinian corals: A new window into past biogeochemical change
X.T. Wang, M.G. Prokopenko, D.M. Sigman, J.F. Adkins, L.F. Robinson, H.A. Ren, S. Oleynik, B. Williams, G.H. Haug
Over the last two decades, the skeletal remains of deep-sea corals have arisen as a geochemical archive of Pleistocene oceanographic change. Here we report the exploration of the isotopic composition of the carbonate-bound organic nitrogen (hereafter, CB-δ15N) in the deep-sea scleractinian coral Desmophyllum dianthus as a possible tool for…
The isotopic composition of diatom-bound nitrogen in Southern Ocean sediments
D.M. Sigman, M.A. Altabet, R. François, D.C. McCorkle, J.-F. Gaillard

Treatment of diatom microfossils from Southern Ocean sediments with hot perchloric acid leaves a diatom-bound N fraction which is 0-4‰ lower in δ15N than the bulk sediment, typically 3‰ lower in recent Antarctic diatom ooze. Results from Southern Ocean surface sediments indicate that early diagenetic changes in bulk sediment N content and δ15N…

Isotopic composition of rainwater nitrate at Bermuda: The influence of air mass source and chemistry in the marine boundary layer
K.E. Altieri, M.G. Hastings, A.R. Gobel, A.J. Peters, D.M. Sigman
Emissions of anthropogenic nitrogen (N) to the atmosphere have increased tenfold since preindustrial times, resulting in increased N deposition to terrestrial and coastal ecosystems. The current sources of N deposition to the ocean, however, are poorly understood. To investigate the sources of nitrate in rainwater deposited to the ocean, two years…
Isotopic composition of skeleton-bound organic nitrogen in reef-building symbiotic corals: A new method and proxy evaluation at Bermuda
X.T. Wang, D.M. Sigman, A.L. Cohen, D.J. Sinclair, R.M. Sherrell, M.A. Weigand, D.V. Erler, H.A. Ren
The skeleton-bound organic nitrogen in reef-building symbiotic corals may be a high-resolution archive of ocean nitrogen cycle dynamics and a tool for understanding coral biogeochemistry and physiological processes. However, the existing methods for measuring the isotopic composition of coral skeleton-bound organic nitrogen (hereafter, CS-δ15N)…
Isotopic constraints on glacial/interglacial changes in the oceanic nitrogen budget
C. Deutsch, D.M. Sigman, R.C. Thunell, A.N. Meckler, G.H. Haug

We investigate the response of the 15N/14N of oceanic nitrate to glacial/interglacial changes in the N budget, using a geochemical box model of the oceanic N cycle that includes N2 fixation and denitrification in the sediments and suboxic water column. This model allows us to quantify the isotopic response of different oceanic nitrate pools to…

Isotopic evidence for a marine ammonium source in rainwater at Bermuda
K.E. Altieri, M.G. Hastings, A.J. Peters, S. Oleynik, D.M. Sigman
Emissions of anthropogenic nitrogen (N) to the atmosphere have increased tenfold since preindustrial times, resulting in increased N deposition to terrestrial and coastal ecosystems. The sources of N deposition to the ocean, however, are poorly understood. Two years of event-based rainwater samples were collected on the island of Bermuda in the…
Isotopic evidence for large gaseous nitrogen losses from tropical rainforests
B.Z. Houlton, D.M. Sigman, L.O. Hedin

The nitrogen isotopic composition (15N/14N) of forested ecosystems varies systematically worldwide. In tropical forests, which are elevated in 15N relative to temperate biomes, a decrease in ecosystem 15N/14N with increasing rainfall has been reported. This trend is seen in a set of well characterized Hawaiian rainforests, across which we have…

Isotopic evidence for nitrification in the Antarctic winter mixed layer
S.M. Smart, S.E. Fawcett, S.J. Thomalla, M.A. Weigand, C.J.C. Reason, D.M. Sigman
We report wintertime nitrogen and oxygen isotope ratios (δ15N and δ18O) of seawater nitrate in the Southern Ocean south of Africa. Depth profile and underway surface samples collected in July 2012 extend from the subtropics to just beyond the Antarctic winter sea ice edge. We focus here on the Antarctic region (south of 50.3°S), where application…
Isotopic evidence for source changes of nitrate in rain at Bermuda
M.G. Hastings, D.M. Sigman, F. Lipschultz

Rainwater collected on the island of Bermuda between January 2000 and January 2001 shows pronounced seasonal variation in the nitrogen and oxygen isotopic composition of nitrate. Higher 15N/14N and lower 18O/16O ratios are observed in the warm season (April-September) in comparison to the cool season (October-March): The mean δ15N of nitrate…

Isotopic ratiometry of nitric oxide using a dual-modulation faraday rotation spectrometer
E.J. Zhang, F. Nuruzzaman, Y. Wang, D.M. Sigman, G. Wysocki
A dual-modulation Faraday rotation spectrometer is employed for isotopic ratiometry of nitric oxide (NO) converted from nitrate/nitrite. Excellent linearity of measured NO to dissolved nitrate is demonstrated. Ratiometry of IAEA-NO-3 standards indicates 3 % accuracy. © 2014 OSA.
Isotopic ratiometry of nitric oxide using a dual-modulation faraday rotation spectrometer
E.J. Zhang, F. Nuruzzaman, Y. Wang, D.M. Sigman, G. Wysocki
A dual-modulation Faraday rotation spectrometer is employed for isotopic ratiometry of nitric oxide (NO) converted from nitrate/nitrite. Excellent linearity of measured NO to dissolved nitrate is demonstrated. Ratiometry of IAEA-NO-3 standards indicates ∼3 % accuracy. © 2014 Optical Society of America.