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
17 Publications
Applied Filters: First Letter Of Title: D Reset
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…
Deep-sea coral evidence for lower Southern Ocean surface nitrate concentrations during the last ice age
X.T. Wang, D.M. Sigman, M.G. Prokopenko, J.F. Adkins, L.F. Robinson, S.K. Hines, J. Chai, A.S. Studer, A. Martínez-García, T. Chen, G.H. Haug
The Southern Ocean regulates the ocean s biological sequestration of CO2 and is widely suspected to underpin much of the ice age decline in atmospheric CO2 concentration, but the specific changes in the region are debated. Although more complete drawdown of surface nutrients by phytoplankton during the ice ages is supported by some sediment core…
Deglacial changes in ocean circulation from an extended radiocarbon calibration
K.A. Hughen, J.T. Overpeck, S.J. Lehman, M. Kashgarian, J.R. Southon, L.C. Peterson, R. Alley, D.M. Sigman

Temporal variations in the atmospheric concentration of radiocarbon sometimes result in radiocarbon-based age-estimates of biogenic material that do not agree with true calendar age. This problem is particularly severe beyond the limit of the high-resolution radiocarbon calibration based on tree-ring data, which stretches back only to about 11…

Deglacial nitrogen isotope changes in the Gulf of Mexico: Evidence from bulk sedimentary and foraminifera-bound nitrogen in Orca Basin sediments
A.N. Meckler, H.A. Ren, D.M. Sigman, N. Gruber, B. Plessen, C.J. Schubert, G.H. Haug

Constraining variations in marine N2-fixation over glacial-interglacial timescales is crucial for determining the role of the marine nitrogen cycle in modifying ocean productivity and climate, yet paleo-records from N2-fixation regions are sparse. Here we present new nitrogen isotope (δ15N) records of bulk sediment and foraminifera test-bound …

Deglacial pulses of deep-ocean silicate into the subtropical North Atlantic Ocean
A.N. Meckler, D.M. Sigman, K.A. Gibson, R. François, A. Martínez-García, S.L. Jaccard, U. Röhl, L.C. Peterson, R. Tiedemann, G.H. Haug
Growing evidence suggests that the low atmospheric CO 2 concentration of the ice ages resulted from enhanced storage of CO 2 in the ocean interior, largely as a result of changes in the Southern Ocean. Early in the most recent deglaciation, a reduction in North Atlantic overturning circulation seems to have driven CO 2 release from the Southern…
Denitrification in anoxic sediments supported by biological nitrate transport
M.G. Prokopenko, D.M. Sigman, W.M. Berelson, D.E. Hammond, B. Barnett, L. Chong, A. Townsend-Small
Biologically available nitrogen (fixed N) is removed from the oceans by metabolic conversion of inorganic N forms (nitrate and ammonium) to N2 gas. Much of this removal occurs in marine sediments, where reaction rates are thought to be limited by diffusion. We measured the concentration and isotopic composition of major dissolved nitrogen species…
Detailed sedimentary N isotope records from Cariaco Basin for terminations I and V: Local and global implications
A.N. Meckler, G.H. Haug, D.M. Sigman, B. Plessen, L.C. Peterson, H.R. Thierstein

For the last deglaciation and Termination V (the initiation of MIS 11 at around 430 ka) we report high-resolution sedimentary nitrogen isotope (δ15N) records from Cariaco Basin in the Caribbean Sea. During both terminations the previously reported interglacial decrease in δ15N clearly lags local changes such as water column anoxia as well as…

Diagenetic aluminum uptake into diatom frustules and the preservation of diatom-bound organic nitrogen
H.A. Ren, B.G. Brunelle, D.M. Sigman, R.S. Robinson
The chemistry and isotopic composition of siliceous diatom frustules and the organic matter bound within them have been used to reconstruct past changes in the environment. However, the alteration of biogenic silica in the sediments and its influence on the chemical properties of the diatom opal and diatom-bound organic matter has not been broadly…
Diatom-bound 15N/14N: New support for enhanced nutrient consumption in the ice age subantarctic
R.S. Robinson, D.M. Sigman, P.J. Difiore, M.M. Rohde, T.A. Mashiotta, D.W. Lea

Diatom-bound 15N/14N was used to reconstruct the glacial nutrient status of the Subantarctic Zone in the Southern Ocean. Down-core records from both the Pacific and Indian sectors show δ 15N of 5 to 6%‰ during the Last Glacial Maximum and a decrease, coincident with the glacial termination, to values as low as 2‰. The effect of either diatom…

Dinitrogen fixation in the world s oceans
D. Karl, A. Michaels, B. Bergman, D. Capone, E. Carpenter, R. Letelier, F. Lipschultz, H. Paerl, D.M. Sigman, L. Stal
The surface water of the marine environment has traditionally been viewed as a nitrogen (N) limited habitat, and this has guided the development of conceptual biogeochemical models focusing largely on the reservoir of nitrate as the critical source of N to sustain primary productivity. However, selected groups of Bacteria, including cyanobacteria,…
Dissolved Organic Nitrogen Cycling in the South China Sea From an Isotopic Perspective
R. Zhang, X.T. Wang, H.A. Ren, J. Huang, M. Chen, D.M. Sigman
Dissolved organic nitrogen (DON) is the dominant form of fixed nitrogen in most low and middle latitude ocean surface waters. Here, we report measurements of DON isotopic composition (δ15N) from the west South China Sea (SCS), with the goal of providing new insight into DON cycling. The concentration of DON in the surface ocean is correlated (r =…
Distinct nitrogen isotopic compositions of healthy and cancerous tissue in mice brain and head&neck micro-biopsies
M. Straub, D.M. Sigman, A. Auderset, J. Ollivier, B. Petit, B. Hinnenberg, F. Rubach, S. Oleynik, M.-C. Vozenin, A. Martínez-García
Background: Cancerous cells can recycle metabolic ammonium for their growth. As this ammonium has a low nitrogen isotope ratio (15N/14N), its recycling may cause cancer tissue to have lower 15N/14N than surrounding healthy tissue. We investigated whether, within a given tissue type in individual mice, tumoral and healthy tissues could be…
The distinct nitrogen isotopic compositions of low and high molecular weight marine DON
A.N. Knapp, D.M. Sigman, A.B. Kustka, S.A. Sañudo-Wilhelmy, D.G. Capone
To constrain the sources and cycling of bulk and size-fractionated marine dissolved organic nitrogen (DON), samples were collected for concentration and isotopic (δ 15N) analysis from the western tropical North Atlantic Ocean as well as over the North Australian shelf. Bulk DON concentrations are typically between 4 and 6μM, with low molecular…
Distinct roles of the Southern Ocean and North Atlantic in the deglacial atmospheric radiocarbon decline
M.P. Hain, D.M. Sigman, G.H. Haug
In the context of the atmospheric CO2 14C/C (δCatm14) changes since the last ice age, two episodes of sharp δCatm14 decline have been related to either the venting of deeply sequestered low-14C CO2 through the Southern Ocean surface or the abrupt onset of North Atlantic Deep Water (NADW) formation. In model simulations using an improved…
Distinguishing between water column and sedimentary denitrification in the Santa Barbara Basin using the stable isotopes of nitrate
D.M. Sigman, R.S. Robinson, A.N. Knapp, A. van Geen, D.C. McCorkle, J.A. Brandes, R.C. Thunell
[1] Below its sill depth, the Santa Barbara Basin (SBB) is commonly suboxic ([O2] ̃ 3 μM), with only brief periods of ventilation. Associated with development of suboxia, the concentration of nitrate decreases with depth into the basin without an associated decrease in phosphate, indicating that a substantial fraction of the nitrate supplied to…
The distribution of nitrate 15N/14N in marine sediments and the impact of benthic nitrogen loss on the isotopic composition of oceanic nitrate
M.F. Lehmann, D.M. Sigman, D.C. McCorkle, J. Granger, S. Hoffmann, G. Cane, B.G. Brunelle
We report 15N/14N ratios of porewater nitrate in sediments from the Bering Sea basin, where microbial nitrate reduction has been identified as a significant sink for fixed nitrogen (N). Strong 15N enrichment in porewater nitrate is observed as one goes deeper in the sediments and nitrate concentration [NO3-] decreases (δ15N generally reaches 25-35…
The dual isotopes of deep nitrate as a constraint on the cycle and budget of oceanic fixed nitrogen
D.M. Sigman, P.J. Difiore, M.P. Hain, C. Deutsch, Y. Wang, D.M. Karl, A.N. Knapp, M.F. Lehmann, S. Pantoja
We compare the output of an 18-box geochemical model of the ocean with measurements to investigate the controls on both the mean values and variation of nitrate δ15N and δ18O in the ocean interior. The δ18O of nitrate is our focus because it has been explored less in previous work. Denitrification raises the δ15N and δ18O of mean ocean nitrate by…