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
11 Publications
Applied Filters: First Letter Of Last Name: A Reset
Southern Ocean upwelling, Earth s obliquity, and glacial-interglacial atmospheric CO2 change
X.E. Ai, A.S. Studer, D.M. Sigman, A. Martínez-García, F. Fripiat, L.M. Thöle, E. Michel, J. Gottschalk, L. Arnold, S. Moretti, M. Schmitt, S. Oleynik, S.L. Jaccard, G.H. Haug
Previous studies have suggested that during the late Pleistocene ice ages, surface-deep exchange was somehow weakened in the Southern Ocean s Antarctic Zone, which reduced the leakage of deeply sequestered carbon dioxide and thus contributed to the lower atmospheric carbon dioxide levels of the ice ages. Here, high-resolution diatom-bound nitrogen…
The southward migration of the Antarctic Circumpolar Current enhanced oceanic degassing of carbon dioxide during the last two deglaciations
X.E. Ai, L.M. Thöle, A. Auderset, M. Schmitt, S. Moretti, A.S. Studer, E. Michel, M. Wegmann, A. Mazaud, P.K. Bijl, D.M. Sigman, A. Martínez-García, S.L. Jaccard
Previous studies suggest that meridional migrations of the Antarctic Circumpolar Current may have altered wind-driven upwelling and carbon dioxide degassing in the Southern Ocean during past climate transitions. Here, we report a quantitative and continuous record of the Antarctic Circumpolar Current latitude over the last glacial-interglacial…
The nitrogen isotope biogeochemistry of sinking particles from the margin of the eastern North Pacific
M.A. Altabet, C. Pilskaln, R. Thunell, C. Pride, D.M. Sigman, F. Chavez, R. François
The nitrogen isotopic composition of time-series sediment trap samples, dissolved NO3/-, and surficial sediments was determined in three regions along the margin of the eastern North Pacific: Monterey Bay, San Pedro Basin, and the Gulf of California (Carmen and Guaymas Basins). Complex physical regimes are present in all three areas, and each is…
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…
Molecular characterization of water soluble organic nitrogen in marine rainwater by ultra-high resolution electrospray ionization mass spectrometry
K.E. Altieri, M.G. Hastings, A.J. Peters, D.M. Sigman

Atmospheric water soluble organic nitrogen (WSON) is a subset of the complex organic matter in aerosols and rainwater, which impacts cloud condensation processes and aerosol chemical and optical properties and may play a significant role in the biogeochemical cycle of N. However, its sources, composition, connections to inorganic N, and…

Marine biogenic source of atmospheric organic nitrogen in the subtropical North Atlantic
K.E. Altieri, S.E. Fawcett, A.J. Peters, D.M. Sigman, M.G. Hastings
Global models estimate that the anthropogenic component of atmospheric nitrogen (N) deposition to the ocean accounts for up to a third of the ocean s external N supply and 10% of anthropogenic CO2 uptake. However, there are few observational constraints from the marine atmospheric environment to validate these findings. Due to the paucity of…
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…
Stable isotopic signature of dissimilatory nitrate reduction is robust against enzyme mutation
C. Asamoto, Y. Ryu, K. Eckartt, J. Kelley-Kern, Lars Dietrich, D.M. Sigman, S.H. Kopf
The proportionality of oxygen-to-nitrogen isotope effects (18ε/15ε) is used as a key isotopic signature of nitrogen cycling processes in the environment. Dissimilatory nitrate reduction is observed to have an 18ε/15ε proportionality of 0.9 in marine and 0.6 in freshwater/terrestrial ecosystems. The origins of this difference are uncertain, with…
Gulf Stream intensification after the early Pliocene shoaling of the Central American Seaway
A. Auderset, A. Martínez-García, R. Tiedemann, A.P. Hasenfratz, T.I. Eglinton, R. Schiebel, D.M. Sigman, G.H. Haug
The shoaling of the Central American Seaway (CAS) around 4.6 Ma (million years ago) is thought to have enhanced the Gulf Stream, strengthening the Atlantic Meridional Overturning Circulation and potentially influencing the evolution of Pliocene climate. Paleoclimate records indicate a buildup of heat and salt in the Caribbean and changes in the…
Enhanced ocean oxygenation during Cenozoic warm periods
A. Auderset, S. Moretti, B. Taphorn, P.-R. Ebner, E.R. Kast, X.T. Wang, R. Schiebel, D.M. Sigman, G.H. Haug, A. Martínez-García

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…

Sea Level Modulation of Atlantic Nitrogen Fixation Over Glacial Cycles
A. Auderset, F. Fripiat, R.C. Creel, L. Oesch, A.S. Studer, J. Repschläger, E. Hathorne, H.B. Vonhof, R. Schiebel, L. Gordon, K. Lawrence, H.A. Ren, G.H. Haug, D.M. Sigman, A. Martínez-García
N2 fixation in low-latitude surface waters dominates the input of fixed nitrogen (N) to the global ocean, sustaining ocean fertility. In the Caribbean Sea, higher foraminifera-bound (FB-)δ15N indicates a decline in N2 fixation during ice ages, but its cause and broader implications are unclear. Here, we report three additional Atlantic FB-δ15N…