About

Daniel M. Sigman is the Dusenbury Professor of Geological and Geophysical Sciences at Princeton University, affiliated with the Department of Geosciences. He is part of the Sigman Research Laboratory at Princeton, where his research focuses on Geochemistry and Paleoclimate. His work involves studying the chemical processes and climate history recorded in geological materials, contributing to the understanding of Earth's past climate and biogeochemical cycles. Sigman has been recognized for his scientific contributions, including election to the National Academy of Sciences. His contact information includes an office phone number 609-258-2194 and an email address, and he maintains a professional profile with an ORCID ID 0000-0002-7923-1973.

Research topics

• Oceanography
• Geology
• Climatology
• Paleontology
• Biology
• Environmental science
• Earth science
• Environmental chemistry
• Chemistry
• Ecology

Selected publications

• Prokaryotic bias in surface ocean particles.

  UNC Libraries · 2026-04-10

  articleOpen access

  While the ocean's photosynthetic production of organic matter rivals that on land, a combination of heterotrophy and sinking prevents significant accumulation of particulate organic matter (POM) in open ocean surface waters. The origins and fates of POM in ocean surface waters are unclear, in part due to the dominance of nonliving, altered material. From the natural nitrogen isotopic composition of chlorophyll and its degradation products, we estimate the fraction of particles from eukaryotic vs. prokaryotic phytoplankton. In subtropical gyres and along the eastern North Pacific margin, the eukaryotic-to-prokaryotic ratio in particles matches that of living phytoplankton. However, in the North Atlantic outside its subtropical gyre, particles have a lower eukaryotic-to-prokaryotic ratio than do the living phytoplankton. This discrepancy at least partly arises from preferential sinking of eukaryotic biomass, consistent with the canonical but disputed paradigm that cyanobacteria disproportionately fulfill the energetic demands of the upper ocean microbial community while eukaryotes drive export production. The prokaryotic bias in surface ocean particles may also result from slow decomposition of specific components of prokaryotic biomass, a possible bottleneck in the ocean's microbial loop. The different fates of organic matter produced by eukaryotic and prokaryotic phytoplankton affect the productivity of the surface ocean, carbon export to the interior, and the signals recorded in deep-sea sediments.

  PublisherDOI

• Prokaryotic bias in surface ocean particles

  Proceedings of the National Academy of Sciences · 2026-04-01

  articleOpen accessSenior author

  While the ocean's photosynthetic production of organic matter rivals that on land, a combination of heterotrophy and sinking prevents significant accumulation of particulate organic matter (POM) in open ocean surface waters. The origins and fates of POM in ocean surface waters are unclear, in part due to the dominance of nonliving, altered material. From the natural nitrogen isotopic composition of chlorophyll and its degradation products, we estimate the fraction of particles from eukaryotic vs. prokaryotic phytoplankton. In subtropical gyres and along the eastern North Pacific margin, the eukaryotic-to-prokaryotic ratio in particles matches that of living phytoplankton. However, in the North Atlantic outside its subtropical gyre, particles have a lower eukaryotic-to-prokaryotic ratio than do the living phytoplankton. This discrepancy at least partly arises from preferential sinking of eukaryotic biomass, consistent with the canonical but disputed paradigm that cyanobacteria disproportionately fulfill the energetic demands of the upper ocean microbial community while eukaryotes drive export production. The prokaryotic bias in surface ocean particles may also result from slow decomposition of specific components of prokaryotic biomass, a possible bottleneck in the ocean's microbial loop. The different fates of organic matter produced by eukaryotic and prokaryotic phytoplankton affect the productivity of the surface ocean, carbon export to the interior, and the signals recorded in deep-sea sediments.

  PublisherOA PDFDOI

• Crustose coralline algae biomineral-bound nitrogen isotopes provide a baseline to reconstruct coral trophic strategies

  Communications Earth & Environment · 2026-04-10

  articleOpen access

  Abstract Coral resilience is shaped by trophodynamic flexibility – the balance between photosymbiont-derived energy and feeding-based heterotrophy – yet quantifying this balance across taxa and through time remains difficult. Nitrogen (N) isotopes are a powerful tool to investigate trophic strategies, but their use requires information on local isotopic baselines. Here, we introduce the biomineral-bound N isotopes of crustose coralline algae (CCA) as an archive that closely tracks the N isotopic composition of the reef nitrate supply, making it a proxy for a reef’s isotopic baseline. Coupled N isotope measurements of co-occurring CCA, symbiont-bearing, and symbiont-barren corals further enable us to quantify a coral’s “trophic enrichment factor,” reflecting the efficiency of the internal N recycling between the coral and its photosymbionts. From this framework, we derive a Reliance on Symbionts Index (RSI) that captures taxonomic and regional variation in mixotrophy, enabling reconstruction of coral trophodynamics in modern and fossil reef systems.

  PublisherOA PDFDOI

• Tracing Ocean Oxygen Dynamics Through Time: A Miocene Perspective

  2025-03-14

  preprintOpen access

  Foraminifera-bound nitrogen isotopes (FB-δ15N) are a powerful tool for reconstructing past oxygen-deficient zones (ODZs). FB-δ15N record the strong isotopic fractionation associated with bacterial water column denitrification that occurs in oxygen-deficient environments, typically characterised by dissolved oxygen concentrations of less than ~5 µM. We applied this oxygen-sensitive proxy across multiple ocean basins during the Miocene, focusing on the Miocene Climatic Optimum (MCO) and Middle Miocene Climate Transition (MMCT), to study the expansions and contractions of tropical ODZs as a response to past global climate change.Our multi-basin analysis indicates nuanced oxygen dynamics, including evidence of a persistent proto-ODZ in the Arabian Sea since ≥19.8 Ma. By integrating FB-δ15N with foraminiferal calcite trace element data (I/Ca, Mn/Ca), we generated the first temporal and spatial record of MMCT deoxygenation in the Arabian Sea. Combining these new data with regional palaeoceanographic proxies, we assess the roles of global climate, regional monsoonal activity, and tectonics in driving Arabian Sea hypoxia, recognising that the contributions of these factors varied in magnitude and timing.In comparison, new preliminary data from the Atlantic and Pacific Oceans suggest synchronised yet regionally distinct ODZ responses during the MCO and subsequent cooling. Our high-resolution reconstructions of Pacific Ocean deoxygenation following the MMCT cooling indicate glacial/interglacial variations and provide critical new insights into potential marine oxygen deficient zone trajectories under future climate scenarios.

  PublisherDOI

• Equatorial upwelling of phosphorus drives Atlantic N2 fixation and Sargassum blooms

  Nature Geoscience · 2025-11-05 · 6 citations

  articleOpen access

  Abstract The Great Atlantic Sargassum Belt first appeared in 2011 and quickly became the largest interconnected floating biome on Earth. In recent years, Sargassum stranding events have caused substantial ecological and socio-economic impacts in coastal communities. Sargassum requires both phosphorus (P) and nitrogen (N) for growth, yet the primary sources of these nutrients fuelling the extensive Sargassum blooms remain unclear. Here we use coral-bound N isotopes to reconstruct N 2 fixation, the ultimate source of the ocean’s bioavailable N, across the Caribbean over the past 120 years. Our data indicate that changes in N 2 fixation were primarily controlled by multidecadal and interannual changes in equatorial Atlantic upwelling of ‘excess P’, that is, P in stoichiometric excess relative to fixed N. We show that the supply of excess P from equatorial upwelling and N from the N 2 fixation response can account for the majority of Sargassum variability since 2011. Sargassum dynamics are best explained by their symbiosis with N 2 -fixing epiphytes, which render the macroalgae highly competitive during strong equatorial upwelling of excess P. Thus, the future of Sargassum in the tropical Atlantic will depend on how global warming affects equatorial Atlantic upwelling and the climatic modes that control it.

  PublisherOA PDFDOI

• Nitrogen isotope ratios across the Bermuda coral reef: implications for coral nitrogen sources and the coral-bound nitrogen isotope proxy

  Frontiers in Marine Science · 2025-03-26 · 4 citations

  articleOpen accessSenior authorCorresponding

  The nitrogen (N) isotopic composition of coral tissue provides insight into N sources and cycling on reefs, and coral skeleton-bound organic matter (CS-δ 15 N) can extend these insights into the past. Across the Bermuda platform, we measured the δ 15 N of four coral species and their potential N sources, as well as an asymbiotic filter feeder as a comparative heterotroph and benthic macroalgae as a comparative autotroph. Organisms and organic N pools from the coral reefs exhibit a δ 15 N increase toward the Bermuda coast, likely due to anthropogenic N inputs. At all sites, the δ 15 N of bulk coral tissue is consistent with corals feeding dominantly on zooplankton-sized organic matter and some smaller suspended particulate N. The corals lack the trophic δ 15 N elevation that characterizes serpulids; this is consistent with internal recycling and retention of low-δ 15 N metabolic N by symbiont-bearing corals. The data are inconsistent with corals’ reliance on the dissolved inorganic N used by macroalgae at the same sites. Among coral species, two species with smaller polyps (1-2 mm) have ~1‰ lower bulk tissue δ 15 N than two counterparts with larger polyps (5-10 mm), perhaps due to differences in food source. Taxon-specific δ 15 N differences are also observed between coral tissue and skeleton-bound N, with larger differences in the two small-polyp species. In net, however, CS-δ 15 N mean values and spatial gradients were similar in the four species studied.

  PublisherOA PDFDOI

• Exploring glacial-interglacial nutrient conditions in the Antarctic Zone: Insights from a one-dimensional water column model

  2025-03-14

  preprintOpen access

  In the Antarctic Zone (AZ), deep nutrient-rich waters ascend to the surface, feeding the Southern Ocean's overturning circulation cells. However, the rate of upwelling exceeds the capacity of phytoplankton to fully consume the gross nutrient supply to the AZ surface, leading to the release of previously sequestered CO2 into the atmosphere. During ice ages, enhanced nutrient utilization has been proposed as a mechanism that could contribute to lower atmospheric CO2 concentration. Fossil-bound δ15N records in the AZ point to a more complete nitrate consumption in surface waters during ice ages. This increase in nitrate utilization coincides with reduced export production, suggesting a lower gross nitrate supply to the surface and, therefore, a reduction in the exchange of water between the surface and the deep ocean. Preliminary reconstructions indicate more than a 5-fold reduction in the rate of gross nitrate supply to match paleo proxy data and near complete nitrate consumption at the surface. Model simulations are ambiguous, but none show more than a ≥ 2-fold reduction in water exchange in the AZ during ice ages.One hypothesis for this discrepancy is the progressive depletion (“mining-out”) of nutrients from the AZ upper ocean. Reduced glacial upwelling, combined with repeated summer nitrate consumption and the export of assimilated nitrate as sinking organic matter, followed by deep winter mixing, could gradually deplete the upper water column’s nutrient reservoir. This process would lower the shallow subsurface nutrient concentrations and elevate nitrate δ15N relative to the deep ocean. As a result, the nutrient supply per volume of upwelled water would decline, aligning better with model simulations. To test this hypothesis, we developed a 1D advection-diffusion-reaction model of the water column, accounting for surface nitrate consumption and isotope fractionation. The model was calibrated using Argo floats data and high-resolution hydrographic nitrate isotopes transect in the AZ (GO-SHIP SO4P 2018), successfully matching depth and seasonal profiles. We also applied the model to the western subarctic Pacific, which exhibits a similar observation pattern for fossil-bound δ15N and export production during ice ages but contrasts in the ratio between advective and diffusive nutrient supply.Our results highlight the critical role of nutrient mining in driving isotopic changes during ice ages. With reduced upwelling, nutrients are progressively depleted in the upper AZ. However, even under this mechanism, a substantial reduction in upwelling (more than a twofold decrease) is still required to achieve observed glacial δ15N values – though less extreme than previous estimates. Nevertheless, in reduced upwelling scenarios, the glacial surface nitrate concentration is significantly higher than previous estimates. This supports the potential of nutrient mining in matching paleo-data with less drastic changes to the Southern Ocean.

  PublisherDOI

• Reduced N2 fixation in the Atlantic Ocean during the Warm Late Pliocene

  Research Square · 2025-06-27

  preprintOpen access
  PublisherOA PDFDOI

• Similar Oxygen Sensitivities of Different Steps of Denitrification in Estuarine Waters

  Environmental Science & Technology · 2025-04-04 · 5 citations

  article

  Hypoxia is observed and projected to expand in many aquatic environments, largely due to excess anthropogenic nutrient inputs and climate change, thus influencing biogeochemical processes. Denitrification, generally an anaerobic process, removes bioavailable nitrogen and produces nitrous oxide (N2O). However, limited observations of the effect of oxygen on denitrification restrict our ability to estimate changes in the amount of bioavailable nitrogen and N2O emissions under anthropogenic perturbations and climate change. Here, we show that all denitrification steps increased, while the N2O production yield from denitrification decreased with decreasing oxygen in Chesapeake Bay – the largest estuary in the United States. The different steps of denitrification responded similarly to oxygen changes in Chesapeake Bay, unlike open ocean oxygen minimum zones, with implications for the accumulation or depletion of denitrification intermediates such as nitrite and N2O. Our observations also suggest that current model parametrizations of denitrification in Chesapeake Bay likely overestimate denitrification and nitrogen removal in the presence of oxygen, which would bias the evaluation of nutrient cycling, ecosystem productivity, and the extent of hypoxia. Overall, our newly derived oxygen sensitivities of denitrification could be used to improve model parametrizations of denitrification and constrain the nitrogen budget and N2O emissions in estuarine and coastal environments experiencing hypoxia.

  PublisherDOI

• Effects of photosymbiosis and related processes on planktic foraminifera-bound nitrogen isotopes in South Atlantic sediments

  Biogeosciences · 2025-04-17 · 4 citations

  articleOpen access

  Abstract. Foraminifera often form symbiotic relationships with photosynthetic algae, providing a host environment and inorganic nutrients in exchange for photosynthetic organic matter from the algal symbiont. To date, the history of this relationship has been studied in paleoceanographic records using the oxygen and carbon stable isotopes of foraminiferal calcite. More recently, photosymbiotic activity has been observed to impact the nitrogen isotope ratio (δ15N) of foraminiferal tissue and the organic matter incorporated into foraminiferal tests. Dinoflagellate symbiont-bearing species appear to be lower in δ15N than symbiont-barren species and more similar to their feeding sources, likely due to their retention of low-δ15N metabolic ammonium and thus a weaker amplitude for the “trophic enrichment factor”, the δ15N increase per trophic level that is widely observed in food webs. We report new glacial–interglacial foraminifera-bound δ15N (FB-δ15N) data from Deep Sea Drilling Program Site 516, located in the subtropical South Atlantic gyre, which contains multiple foraminifera species at adequately high abundance for interspecies comparison of foraminiferal nitrogen, carbon, and oxygen isotopes over a full glacial cycle. Our data show a conserved δ15N difference of 3 ‰–5 ‰ between dinoflagellate-bearing species and the other species, qualitatively consistent with, but greater in amplitude than, the δ15N difference observed in previous modern ocean and core-top studies. We propose that this greater amplitude at Site 516 is the result of the lateral transport of symbiont-barren species into the South Atlantic subtropical gyre, which appears to represent a small region of low thermocline nitrate δ15N surrounded by regions with higher thermocline nitrate δ15N. We demonstrate that FB-δ15N provides a clear signal of dinoflagellate endosymbiosis and that it may be able to identify other, weaker endosymbioses (e.g., with chrysophytes or pelagophytes). However, the data also suggest caution in regions with strong gradients, where species from contrasting environments may occur in a single sediment sample.

  PublisherOA PDFDOI

Recent grants

• Collaborative Research: Identifying the Role of Basin-scale Climate Variability in the Decline of Atlantic Corals

  NSF · $265k · 2015–2018

• MRI: Acquisition of Stable Isotope Instrumentation for the Biogeosciences at Princeton University

  NSF · $516k · 2009–2012

• Collaborative research: Non-Local Bacterial Transport of Nitrate within Sediments Underlying Oxygen Deficient Zones: A new Twist in the N Cycle

  NSF · $109k · 2007–2011

• Application of a New Method for Isotopic Analysis of Diatom Microfossil-bound Nitrogen

  NSF · $350k · 2005–2009

• Collaborative Research: GEOTRACES Atlantic Section Nitrate Isotope Measurements

  NSF · $271k · 2010–2013

Frequent coauthors

• Gerald H. Haug

  297 shared

• Alfredo Martínez‐García

  169 shared

• Samuel L. Jaccard

  University of Lausanne

  122 shared

• Haojia Ren

  National Taiwan University

  88 shared

• Alexandra Auderset

  Max Planck Institute for Chemistry

  74 shared

• Anja S Studer

  57 shared

• François Fripiat

  Université Libre de Bruxelles

  55 shared

• Sarah E. Fawcett

  University of Cape Town

  51 shared

Labs

• The Sigman Research Laboratory at Princeton UniversityPI

Education

• Ph.D. MIT/WHOI Joint Program in Oceanography, Marine Geology and Geophysics

  Massachusetts Institute of Technology

  1997

• Bachelor of Science, Geology

  Stanford University

  1991

Awards & honors

• Member of the National Academy of Sciences