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
12 Publications
Applied Filters: First Letter Of Last Name: L Reset
Time-transgressive North Atlantic productivity changes upon Northern Hemisphere glaciation
K.T. Lawrence, D.M. Sigman, T.D. Herbert, C.A. Riihimaki, C.T. Bolton, A. Martínez-García, A. Rosell-Mele, G.H. Haug
Marine biological export productivity declined in high-latitude regions in the North Pacific and Southern Ocean 2.7 million years ago, in parallel with the intensification of Northern Hemisphere glaciation. Here we present data from the North Atlantic, which show a similar but time-transgressive pattern of high-latitude productivity decline from 3…
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…
Origin of the deep Bering Sea nitrate deficit: Constraints from the nitrogen and oxygen isotopic composition of water column nitrate and benthic nitrate fluxes
M.F. Lehmann, D.M. Sigman, D.C. McCorkle, B.G. Brunelle, S. Hoffmann, M. Kienast, G. Cane, J. Clement
On the basis of the normalization to phosphate, a significant amount of nitrate is missing from the deep Bering Sea (BS). Benthic denitrification has been suggested previously to be the dominant cause for the BS nitrate deficit. We measured water column nitrate 15N/14N and 18O/16O as integrative tracers of microbial denitrification, together with…
Coupling the 15N/14N and 18O/ 16O of nitrate as a constraint on benthic nitrogen cycling
M.F. Lehmann, D.M. Sigman, W.M. Berelson
We report 15N/14N and 18O/16O ratios of nitrate in benthic chamber incubations in the continental shelf sediments of the Santa Monica Bay (SMB) to deconvolve the effects of nitrification and denitrification. Estimates of denitrification rate from benthic flux stoichiometry range from 0.9 to 2.5 mmol N m-2 d -1. Between 46% and 100% of the total…
Nitrogen isotopes in tooth enamel record diet and trophic level enrichment: Results from a controlled feeding experiment
J.N. Leichliter, T. Lüdecke, A.D. Foreman, N.N. Duprey, D.E. Winkler, E.R. Kast, H.B. Vonhof, D.M. Sigman, G.H. Haug, M. Clauss, T. Tütken, A. Martínez-García
Nitrogen isotope ratios (δ15N) are a well-established tool for investigating the dietary and trophic behavior of animals in terrestrial and marine food webs. To date, δ15N values in fossils have primarily been measured in collagen extracted from bone or dentin, which is susceptible to degradation and rarely preserved in deep time (>100,000…
Tooth enamel nitrogen isotope composition records trophic position: a tool for reconstructing food webs
J.N. Leichliter, T. Lüdecke, A.D. Foreman, N. Bourgon, N.N. Duprey, H.B. Vonhof, V. Souksavatdy, A.-M. Bacon, D.M. Sigman, T. Tütken, A. Martínez-García

Nitrogen isotopes are widely used to study the trophic position of animals in modern food webs; however, their application in the fossil record is severely limited by degradation of organic material during fossilization. In this study, we show that the nitrogen isotope composition of organic matter preserved in mammalian tooth enamel …

Sensitivity of δ15N of nitrate, surface suspended and deep sinking particulate nitrogen to seasonal nitrate depletion in the Southern Ocean
M.J. Lourey, T.W. Trull, D.M. Sigman
We report measurements of the δ15N of nitrate, suspended particulate nitrogen (PN), and sinking PN from cruises and moored sediment traps in the Subantarctic Zone (SAZ) and Polar Frontal Zone (PFZ) south of Australia. As expected, surface water nitrate δ15N increased as nitrate was consumed during the spring/summer bloom. In contrast, the seasonal…
Carbon, nitrogen, and oxygen stable isotopes in modern tooth enamel: A case study from Gorongosa National Park, central Mozambique
T. Lüdecke, J.N. Leichliter, V. Aldeias, M. Bamford, D. Biro, D. Braun, C. Capelli, J.D. Cybulski, Nicolas Duprey, M. da Silva, A.D. Foreman, Jörg Habermann, G.H. Haug, F. Martínez, J. Mathe, A. Mulch, D.M. Sigman, H.B. Vonhof, R. Bobe, S. Carvalho, A. Martínez-García
The analyses of the stable isotope ratios of carbon (δ13C), nitrogen (δ15N), and oxygen (δ18O) in animal tissues are powerful tools for reconstructing the feeding behavior of individual animals and characterizing trophic interactions in food webs. Of these biomaterials, tooth enamel is the hardest, most mineralized vertebrate tissue and therefore…
Australopithecus at Sterkfontein did not consume substantial mammalian meat
T. Lüdecke, J.N. Leichliter, D. Stratford, D.M. Sigman, H.B. Vonhof, G.H. Haug, M. Bamford, A. Martínez-García

Incorporation of animal-based foods into early hominin diets has been hypothesized to be a major catalyst of many important evolutionary events, including brain expansion. However, direct evidence of the onset and evolution of animal resource consumption in hominins remains elusive. The nitrogen-15 to nitrogen-14 ratio of collagen provides…

Controls on the nitrogen isotopic composition of fish otolith organic matter: Lessons from a controlled diet switch experiment
J.A. Lueders-Dumont, A.G. Forden, E.R. Kast, J.A. Mohan, B.D. Walther, D.M. Sigman, B.B. Ward

The nitrogen isotopes (δ15N) in the organic fraction of accretionary hard part structures, such as fish otoliths, may provide life histories of dietary change. We performed controlled experiments to validate the dynamics of the isotopic signal incorporation into biominerals following dietary shifts and also compared whole-otolith and serial…

Comparison of the isotopic composition of fish otolith-bound organic N with host tissue
J.A. Lueders-Dumont, D.M. Sigman, B.J. Johnson, O.P. Jensen, S. Oleynik, B.B. Ward
The15N/14N ratio of the fish-native organic matter preserved in fish otoliths (or δ15Noto) may allow for reconstruction of fish trophic history and changes in food webs. To support this application, ground-truthing data are needed on the relationships among the δ15N of diet, of fish tissue (e.g., white muscle tissue, δ15Nwmt), and δ15Noto. Using a…
Nitrogen isotopic analysis of carbonate-bound organic matter in modern and fossil fish otoliths
J.A. Lueders-Dumont, X.T. Wang, O.P. Jensen, D.M. Sigman, B.B. Ward
The nitrogen isotopic composition (δ15N) of otolith-bound organic matter (OM) is a potential source of information on dietary history of bony fishes. In contrast to the δ15N of white muscle tissue, the most commonly used tissue for ecological studies, the δ15N of otolith-bound OM (δ15Noto) provides a record of whole life history. More importantly,…