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
13 Publications
Applied Filters: First Letter Of Last Name: D Reset
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…

Effect of global ocean temperature change on deep ocean ventilation
A.M. De Boer, D.M. Sigman, J.R. Toggweiler, J.L. Russell

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…

Controls on sedimentary nitrogen isotopes along the Chile margin
R. De Pol-Holz, R.S. Robinson, D. Hebbeln, D.M. Sigman, O. Ulloa
Chilean margin sedimentary N isotope records have been the focus of paleoceanographic studies examining the extent of water-column denitrification in the eastern South Pacific in the past. Here we use 15N/14N of nitrate and surface sedimentary N along the Chilean coast to investigate the relative contributions of water-column denitrification and…
Links between tropical rainfall and North Atlantic climate during the last glacial period
G. Deplazes, A. Lückge, L.C. Peterson, A. Timmermann, Y. Hamann, K.A. Hughen, U. Röhl, C. Laj, M.A. Cane, D.M. Sigman, G.H. Haug
During the last glacial period, the North Atlantic regionexperienced pronounced, millennial-scale alternations between cold, stadial conditions and milder interstadial conditions - commonly referred to as Dansgaard-Oeschger oscillations - as well as periods of massive iceberg discharge known as Heinrich events1. Changes in Northern Hemisphere…
Spatial coupling of nitrogen inputs and losses in the ocean
C. Deutsch, J.L. Sarmiento, D.M. Sigman, N. Gruber, J.P. Dunne
Nitrogen fixation is crucial for maintaining biological productivity in the oceans, because it replaces the biologically available nitrogen that is lost through denitrification. But, owing to its temporal and spatial variability, the global distribution of marine nitrogen fixation is difficult to determine from direct shipboard measurements. This…
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…

Poleward decrease in the isotope effect of nitrate assimilation across the Southern Ocean
P.J. Difiore, D.M. Sigman, K.L. Karsh, T.W. Trull, R.B. Dunbar, R.S. Robinson
Recent studies provide seasonally and spatially resolved information on the isotopic characteristics of nitrate supply and N cycling in Southern Ocean surface waters. The new data improve our understanding of the nitrate supply to the Antarctic surface and its isotopic characteristics, especially with regard to the summertime subsurface minimum…
Upper ocean nitrogen fluxes in the Polar Antarctic Zone: Constraints from the nitrogen and oxygen isotopes of nitrate
P.J. Difiore, D.M. Sigman, R.B. Dunbar
We report nitrate nitrogen (N) and oxygen (O) isotope measurements from the seasonally sea ice covered Polar Antarctic Zone (PAZ) south of the Southern Antarctic Circumpolar Front. The 15N/14N and 18O/16O ratios of nitrate both increase into the summertime surface mixed layer, in strong correlation with the upward decrease in nitrate concentration…
Nitrogen isotope constraints on subantarctic biogeochemistry
P.J. Difiore, D.M. Sigman, T.W. Trull, M.J. Lourey, K. Karsh, G. Cane, R. Ho
We report nitrate (NO3-) nitrogen isotope ratios for seawater samples collected in the Subantarctic Zone of the Southern Ocean during both winter and summer as part of the Australian Antarctic CRC Subantarctic Zone (SAZ) Project. The concentration and 15N/14N of the wintertime surface nitrate are very close to those of the subantarctic thermocline…
Biogenic-to-lithogenic handoff of particulate Zn affects the Zn cycle in the Southern Ocean
J. Duan, R. Cloete, J.C. Loock, A. Lanzirotti, M. Newville, A. Martínez-García, D.M. Sigman, P.J. Lam, A.N. Roychoudhury, S.C.B. Myneni
Zinc (Zn) is vital to marine organisms. Its active uptake by phytoplankton results in a substantial depletion of dissolved Zn, and Zn bound to particulate organic matter replenishes dissolved Zn in the ocean through remineralization. However, we found that particulate Zn changes from Zn bound to phosphoryls in cells to recalcitrant inorganic pools…
Megacity development and the demise of coastal coral communities: Evidence from coral skeleton δ15N records in the Pearl River estuary
N.N. Duprey, X.T. Wang, T. Kim, J.D. Cybulski, H.B. Vonhof, P.J. Crutzen, G.H. Haug, D.M. Sigman, A. Martínez-García, D.M. Baker
Historical coral skeleton (CS) δ18O and δ15N records were produced from samples recovered from sedimentary deposits, held in natural history museum collections, and cored into modern coral heads. These records were used to assess the influence of global warming and regional eutrophication, respectively, on the decline of coastal coral communities…
Life and death of a sewage treatment plant recorded in a coral skeleton Δ15N record
N.N. Duprey, X.T. Wang, P.D. Thompson, J.E. Pleadwell, L.J. Raymundo, K. Kim, D.M. Sigman, D.M. Baker
We investigated the potential of coral skeleton δ15N (CS-δ15N) records for tracking anthropogenic-N sources in coral reef ecosystems. We produced a 56 yr-long CS-δ15N record (1958–2014) from a reef flat in Guam that has been exposed to varying 1) levels of sewage treatment 2) population density, and 3) land use. Increasing population density (from…
Decadal oscillations in the ocean s largest oxygen-deficient zone
N.N. Duprey, A.D. Foreman, J.D. Carriquiry, C.D. Charles, S.C. Sanchez, H.B. Vonhof, F. Rubach, R. Rabenstein, M. Rohr, H. Reyes-Bonilla, D. Marconi, D.M. Sigman, G.H. Haug, A. Martínez-García
The impact of global warming on the ocean s oxygen-deficient zones (ODZs) is uncertain, partly because of a lack of data on past changes. We report monthly resolved records of coral skeleton-bound nitrogen isotopes (CS-δ15N) to reconstruct denitrification in the Eastern Tropical North Pacific (ETNP) ODZ over the last 80 years. The data indicate…