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
14 Publications
Applied Filters: First Letter Of Title: A Reset
An abrupt wind shift in western Europe at the onset of the Younger Dryas cold period
A. Brauer, G.H. Haug, P. Dulski, D.M. Sigman, J.F.W. Negendank
The Younger Dryas cooling 12,700 years ago is one of the most abrupt climate changes observed in Northern Hemisphere palaeoclimate records. Annually laminated lake sediments are ideally suited to record the dynamics of such abrupt changes, as the seasonal deposition responds immediately to climate, and the varve counts provide an accurate estimate…
Active Pacific meridional overturning circulation (PMOC) during the warm Pliocene
N.J. Burls, A.V. Fedorov, D.M. Sigman, S.L. Jaccard, R. Tiedemann, G.H. Haug
An essential element of modern ocean circulation and climate is the Atlantic meridional overturning circulation (AMOC), which includes deep-water formation in the subarctic North Atlantic. However, a comparable overturning circulation is absent in the Pacific, the world’s largest ocean, where relatively fresh surface waters inhibit North Pacific…
Advances in planktonic foraminifer research: New perspectives for paleoceanography
R. Schiebel, S.M. Smart, A. Jentzen, L. Jonkers, R. Morard, J. Meilland, E. Michel, H.K. Coxall, P.M. Hull, T. de Garidel-Thoron, T. Aze, F. Quillévéré, H. Ren, D.M. Sigman, H.B. Vonhof, A. Martínez-García, M. Kučera, J. Bijma, H.J. Spero, G.H. Haug
Planktonic foraminifer tests are major archives of environmental change and provide a multitude of proxies in paleoceanography and paleoclimatology. The application of such proxies is contingent upon a collaborative effort to better understand how the living organisms record the properties of their environment and how the resulting signals are…
Aerobic respiration along isopycnals leads to overestimation of the isotope effect of denitrification in the ocean water column
D. Marconi, S. Kopf, P.A. Rafter, D.M. Sigman
The nitrogen (N) isotopes provide an integrative geochemical tool for constraining the fixed N budget of the ocean. However, N isotope budgeting requires a robust estimate for the organism-scale nitrogen isotope effect of denitrification, in particular as it occurs in water column denitrification zones (εwcd). Ocean field data interpreted with the…
The Agulhas Current Transports Signals of Local and Remote Indian Ocean Nitrogen Cycling
T. Marshall, D. Sigman, L. Beal, A. Foreman, A. Martínez-García, S. Blain, E. Campbell, F. Fripiat, R. Granger, E. Harris, G.H. Haug, D. Marconi, S. Oleynik, P.A. Rafter, R. Roman, K. Sinyanya, S.M. Smart, S.E. Fawcett

The greater Agulhas Current region is an important component of the climate system, yet its influence on carbon and nutrient cycling is poorly understood. Here, we use nitrate isotopes (δ15N, δ18O, Δ(15–18) = δ15N–δ18O) to trace regional water mass circulation and investigate nitrogen cycling in the Agulhas Current and adjacent recirculating…

Analysis of nitric oxide isotopes via differential faraday rotation spectroscopy
E.J. Zhang, D.M. Sigman, G. Wysocki
We present real-time optical polarization subtraction for calibration of Faraday rotation spectra. Noise analysis yields minor isotope sensitivity of 3.0 ppbv·Hz-1/2 and 1.7×10-8 rad·Hz-1/2 noise-equivalent angle. Sub-permil ratiometric precision is achieved at integration times >100 s. © 2016 OSA.
Analytical improvements and assessment of long-term performance of the oxidation–denitrifier method
S. Moretti, N.N. Duprey, A.D. Foreman, A. Arns, S. Brömme, J. Jung, X.E. Ai, A. Auderset, A.L. Bieler, C. Eck, J. Farmer, B. Hinnenberg, M. Lacerra, J. Leichliter, T. Lüdecke, S. Oleynik, F. Rubach, M. Schmitt, M. Vink, T. Wald, M. Yehudai, D.M. Sigman, A. Martínez-García
The analysis of the nitrogen (N) isotopic composition of organic matter bound to fossil biomineral structures (BB-δ15N) using the oxidation–denitrifier (O–D) method provides a novel tool to study past changes in N cycling processes. Methods: We report a set of methodological improvements to the O–D method, including (a) a method for sealing the…
The Angola Gyre is a hotspot of dinitrogen fixation in the South Atlantic Ocean
T. Marshall, J. Granger, K.L. Casciotti, K. Dähnke, K.-C. Emeis, D. Marconi, M.R. McIlvin, A.E. Noble, M.A. Saito, D.M. Sigman, S.E. Fawcett

Biological dinitrogen fixation is the major source of new nitrogen to marine systems and thus essential to the ocean’s biological pump. Constraining the distribution and global rate of dinitrogen fixation has proven challenging owing largely to uncertainty surrounding the controls thereon. Existing South Atlantic dinitrogen fixation rate…

Antarctic Stratification, Atmospheric Water Vapor, and Heinrich Events: A Hypothesis for Late Pleistocene Deglaciations
D.M. Sigman, A.M. De Boer, G.H. Haug

We have previously argued that the Antarctic and subarctic North Pacific are stratified during ice ages, causing to a large degree the observed low CO2 levels of ice age atmospheres by sequestering respired CO2 in the ocean abyss. Here, we suggest a mechanism for the major deglaciations of the late Pleistocene. The mechanism begins with…

Antarctic Zone nutrient conditions during the last two glacial cycles
A.S. Studer, D.M. Sigman, A. Martínez-García, V. Benz, G. Winckler, G. Kuhn, O. Esper, F. Lamy, S.L. Jaccard, L. Wacker, S. Oleynik, R. Gersonde, G.H. Haug
In a sediment core from the Pacific sector of the Antarctic Zone (AZ) of the Southern Ocean, we report diatom-bound N isotope (δ15Ndb) records for total recoverable diatoms and two distinct diatom assemblages (pennate and centric rich). These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the…
Arctic Ocean stratification set by sea level and freshwater inputs since the last ice age
J.R. Farmer, D.M. Sigman, J. Granger, O.M. Underwood, F. Fripiat, T.M. Cronin, A. Martínez-García, G.H. Haug
Salinity-driven density stratification of the upper Arctic Ocean isolates sea-ice cover and cold, nutrient-poor surface waters from underlying warmer, nutrient-rich waters. Recently, stratification has strengthened in the western Arctic but has weakened in the eastern Arctic; it is unknown if these trends will continue. Here we present…
Assimilation of upwelled nitrate by small eukaryotes in the Sargasso Sea
S.E. Fawcett, M.W. Lomas, J.R. Casey, B.B. Ward, D.M. Sigman
Phytoplankton growth is potentially limited by the scarcity of biologically available forms of nitrogen such as nitrate and ammonium. In the subtropical ocean gyres, water column stratification impedes the upward flux of nitrate to surface waters. Phytoplankton in these waters are assumed to rely largely on ammonium and other forms of nitrogen…
Atlantic dominance of the meridional overturning circulation
A.M. De Boer, J.R. Toggweiler, D.M. Sigman
North Atlantic (NA) deep-water formation and the resulting Atlantic meridional overturning cell is generally regarded as the primary feature of the global overturning circulation and is believed to be a result of the geometry of the continents. Here, instead, the overturning is viewed as a global energy-driven system and the robustness of NA…
Atmospheric deposition of inorganic and organic nitrogen and base cations in Hawaii
J.H. Carrillo, M.G. Hastings, D.M. Sigman, B.J. Huebert
Atmospheric deposition of nitrogen (N) and base cations was measured for 5-7 years on the island of Hawaii and for 1.5 years on Kauai. On Hawaii, mean annual fluxes of K+, Mg2+, and Ca2+ were 15, 17, and 13 kg ha-1 yr-1, respectively. Fog interception was the largest deposition pathway. Sea salt contributed the majority of cations, although…