Roberta Hansman

Woods Hole Oceanographic Institution | WHOI · Department of Geology and Geophysics

Radioisotopes have been used in earth and environmental sciences for over 150 years and provide unique tools to study environmental processes in great detail from a cellular level through to an oceanic basin scale. These nuclear techniques have been employed to understand coastal and marine ecosystems via laboratory and field studies in terms of ho...

The vast majority of freshly produced oceanic dissolved organic carbon (DOC) is derived from marine phytoplankton, then rapidly recycled by heterotrophic microbes. A small fraction of this DOC survives long enough to be routed to the interior ocean, which houses the largest and oldest DOC reservoir. DOC reactivity depends upon its intrinsic chemica...

Ammonia‐oxidizing archaea (AOA) constitute a considerable fraction of microbial biomass in the global ocean, comprising 20‐40% of the ocean's prokaryotic plankton. However, it remains enigmatic to what extent these chemolithoautotrophic archaea release dissolved organic carbon (DOC). A combination of targeted and untargeted metabolomics was used to...

Global environmental changes are challenging the structure and functioning of ecosystems. However, a mechanistic understanding of how global environmental changes will affect ecosystems is still lacking. The complex and interacting biological and physical processes spanning vast temporal and spatial scales that constitute an ecosystem make this a f...

Ammonia-oxidizing archaea (AOA) constitute a considerable fraction of microbial biomass in the global ocean, comprising 20-40% of the ocean's prokaryotic plankton and thus play an important role in global nitrogen cycle. However, it remains enigmatic to what extent these chemolithoautotrophic archaea are releasing dissolved organic matter (DOM). A...

To better understand bioaccumulation of radiocaesium in the commercially important Japanese flatfish, Paralichthys olivaceus, the uptake and depuration kinetics of caesium via both seawater and food were assessed simultaneously using controlled aquaria. The pre-conditioned fish were exposed to radionuclides via the two different pathways (aqueous v...

Improving the Application of Radionuclides in Studies of the Carbon Cycle and the Impact of Ocean Acidification; Monaco, 19–21 October 2016

The potential influence of methane seeps on carbon cycling is a key question for global assessments, but the study of carbon cycling in surface sediments and the water column of cold seep environments is complicated by the high temporal and spatial variability of fluid and gas fluxes at these sites. In this study we directly examined carbon sources...

Supplementary material.

Fig. S1. Principal components analysis from masses with assigned molecular formulas of SPE-DOM from MEDEA samples, color-coded by water mass as indicated. Triangles denote samples collected on MEDEA-1, and squares are from MEDEA-2. Fig. S2. Van Krevelen diagrams showing ratios of hydrogen-to-carbon (H/C) and oxygen-to-carbon (O/C) for assigned mole...

Supplementary tables.

Our recent finding that dilution limits dissolved organic carbon (DOC) utilization in the deep ocean has been criticized based on the common misconception that lability equates to rapid and complete utilization. Even when considering the redefinition of recalcitrant DOC recently proposed by Jiao et al., the dilution hypothesis best explains our exp...

The carbon isotope ratio (δ13C value) of marine particulates is a potentially useful tracer for elucidating pathways of carbon flow in the marine environment. Different species of phytoplankton vary in fractionation vs. CO2 by up to 24‰ in laboratory cultures under varying nutrient and growth conditions, a signal that should propagate through the m...

Characterizing the composition of marine dissolved organic matter (DOM) is important for gaining insight into its role in oceanic biogeochemical cycles. Using Fourier transform ion cyclotron resonance mass spectrometry, we analyzed the molecular composition of solid phase extracted (SPE) DOM from the northeast Atlantic to investigate the specificit...

Oceanic dissolved organic carbon (DOC) is the second largest reservoir of organic carbon in the biosphere. About 72% of the global DOC inventory is stored in deep oceanic layers for years to centuries, supporting the current view that it consists of materials resistant to microbial degradation. An alternative hypothesis is that deep-water DOC consi...

The deep sea is often viewed as a vast, dark, remote, and inhospitable environment, yet the deep ocean and seafloor are crucial to our lives through the services that they provide. Our understanding of how the deep sea functions remains limited, but when treated synoptically, a diversity of supporting, provisioning, regulating and cultural services...

The deep sea is often viewed as a vast, dark, remote, and inhospitable environment, yet the deep ocean and seafloor are crucial to our lives through the services and provisions that they provide. Our understanding of how the deep sea functions remains limited, but when treated synoptically, a diversity of provisioning, regulating and cultural servi...

Sixty percent of the world ocean by area is contained in oligotrophic gyres [Longhurst A (1995) Prog Oceanog 36:77-16], the biomass of which is dominated by picophytoplankton, including cyanobacteria and picoeukaryotic algae, as well as picoheterotrophs. Despite their recognized importance in carbon cycling in the surface ocean, the role of small c...

The Loihi hydrothermal plume provides an opportunity to investigate iron (Fe) oxidation and microbial processes in a system that is truly Fe dominated and distinct from mid-ocean ridge spreading centers. The lack of hydrogen sulfide within the Loihi hydrothermal fluids and the presence of an oxygen minimum zone at this submarine volcano's summit, r...

This paper synthesizes recent findings regarding microbial distributions and processes in the bathypelagic ocean (depth 4 1000 m). Abundance, production and respiration of prokaryotes reflect supplies of particulate and dissolved organic matter to the bathypelagic zone. Better resolution of carbon fluxes mediated by deep microbes requires further t...

Several lines of evidence indicate that microorganisms in the meso- and bathypelagic ocean are metabolically active and respiring carbon. In addition, growing evidence suggests that archaea are fixing inorganic carbon in this environment. However, direct quantification of the contribution from deep ocean carbon sources to community production in th...