Mesoscale iron-enrichment in the open ocean-pumping CO2 into the deep ocean by acceleration of phytoplankton production

Abstract. Continental shelves play a key role in the cycling of nitrogen and carbon. Here the physical transport and biogeochemical transformation processes affecting the fluxes into and out of continental shelf systems are reviewed, and their role in the global cycling of both elements is discussed. Uncertainties in observation-based estimates of nitrogen and carbon fluxes mostly result from uncertainties in the shelf-open ocean exchange of organic and inorganic matter, which is hard to quantify based on observations alone, but can be inferred from biogeochemical models. Model-based nitrogen and carbon budgets are presented for the Northwestern North Atlantic continental shelf. Results indicate that shelves are an important sink for fixed nitrogen and a source of alkalinity, but are not much more efficient in exporting organic carbon to the deep ocean than the adjacent open ocean for the shelf region considered.

Download Full-text

The role of continental shelves in nitrogen and carbon cycling: Northwestern North Atlantic case study

Ocean Science ◽

10.5194/os-6-539-2010 ◽

2010 ◽

Vol 6 (2) ◽

pp. 539-548 ◽

Cited By ~ 39

Author(s):

K. Fennel

Keyword(s):

Continental Shelf ◽

North Atlantic ◽

Deep Ocean ◽

Open Ocean ◽

Biogeochemical Models ◽

Inorganic Matter ◽

Continental Shelves ◽

Shelf Region

Abstract. Continental shelves play a key role in the cycling of nitrogen and carbon. Here the physical transport and biogeochemical transformation processes affecting the fluxes into and out of continental shelf systems are reviewed, and their role in the global cycling of both elements is discussed. Uncertainties in the magnitude of organic and inorganic matter exchange between shelves and the open ocean is a major source of uncertainty in observation-based estimates of nitrogen and carbon fluxes. The shelf-open ocean exchange is hard to quantify based on observations alone, but can be inferred from biogeochemical models. Model-based nitrogen and carbon budgets are presented for the Northwestern North Atlantic continental shelf. Results indicate that shelves are an important sink for fixed nitrogen and a source of alkalinity, but are not much more efficient in exporting organic carbon to the deep ocean than the adjacent open ocean for the shelf region considered.

Download Full-text

What prevents nitrogen depletion in the oxygen minimum zone of the eastern tropical South Pacific?

Biogeosciences ◽

10.5194/bg-12-1113-2015 ◽

2015 ◽

Vol 12 (4) ◽

pp. 1113-1130 ◽

Cited By ~ 7

Author(s):

B. Su ◽

M. Pahlow ◽

H. Wagner ◽

A. Oschlies

Keyword(s):

Nitrogen Fixation ◽

Ocean Circulation ◽

Deep Ocean ◽

South Pacific ◽

Open Ocean ◽

Nitrogen Depletion ◽

Biogeochemical Models ◽

Model Domain ◽

Limiting Nutrient ◽

Oxygen Minimum

Abstract. Local coupling between nitrogen fixation and denitrification in current biogeochemical models could result in runaway feedback in open-ocean oxygen minimum zones (OMZs), eventually stripping OMZ waters of all fixed nitrogen. This feedback does not seem to operate at full strength in the ocean, as nitrate does not generally become depleted in open-ocean OMZs. To explore in detail the possible mechanisms that prevent nitrogen depletion in the OMZ of the eastern tropical South Pacific (ETSP), we develop a box model with fully prognostic cycles of carbon, nutrients and oxygen in the upwelling region and its adjacent open ocean. Ocean circulation is calibrated with Δ14C data of the ETSP. The sensitivity of the simulated nitrogen cycle to nutrient and oxygen exchange and ventilation from outside the model domain and to remineralization scales inside an OMZ is analysed. For the entire range of model configurations explored, we find that the fixed-N inventory can be stabilized at non-zero levels in the ETSP OMZ only if the remineralization rate via denitrification is slower than that via aerobic respiration. In our optimum model configuration, lateral oxygen supply into the model domain is required at rates sufficient to oxidize at least about one fifth of the export production in the model domain to prevent anoxia in the deep ocean. Under these conditions, our model is in line with the view of phosphate as the ultimate limiting nutrient for phytoplankton, and implies that for the current notion of nitrogen fixation being favoured in N-deficit waters, the water column of the ETSP could even be a small net source of nitrate.

Download Full-text

Changes in iron concentrations and bio-availability during an open-ocean mesoscale iron enrichment in the western subarctic Pacific, SEEDS II

Deep Sea Research Part II Topical Studies in Oceanography ◽

10.1016/j.dsr2.2009.06.006 ◽

2009 ◽

Vol 56 (26) ◽

pp. 2796-2809 ◽

Cited By ~ 14

Author(s):

Jun Nishioka ◽

Shigenobu Takeda ◽

Yoshiko Kondo ◽

Hajime Obata ◽

Takashi Doi ◽

...

Keyword(s):

Open Ocean ◽

Subarctic Pacific ◽

Iron Enrichment ◽

Western Subarctic Pacific ◽

Iron Concentrations

Download Full-text

Deep Ocean Water, Artificial Upwelling, and Open Ocean Mariculture: A Promise for the Future

OCEANS 91 Proceedings ◽

10.1109/oceans.1991.613930 ◽

2005 ◽

Author(s):

K.R. McKinley ◽

P.K. Takahashi

Keyword(s):

Deep Ocean ◽

Open Ocean ◽

Ocean Water ◽

Deep Ocean Water ◽

The Future

Download Full-text

Transport Processes in the Gulf of Mexico Along the River-Estuary-Shelf-Ocean Continuum: a Review of Research from the Gulf of Mexico Research Initiative

Estuaries and Coasts ◽

10.1007/s12237-021-01005-1 ◽

2021 ◽

Author(s):

Dubravko Justić ◽

Villy Kourafalou ◽

Giulio Mariotti ◽

Songjie He ◽

Robert Weisberg ◽

...

Keyword(s):

Gulf Of Mexico ◽

Harmful Algal Blooms ◽

Algal Blooms ◽

River Estuary ◽

Deep Ocean ◽

Open Ocean ◽

Transport Processes ◽

Spatial And Temporal Scales ◽

Research Initiative ◽

New Findings

AbstractEstuarine and coastal geomorphology, biogeochemistry, water quality, and coastal food webs in river-dominated shelves of the Gulf of Mexico (GoM) are modulated by transport processes associated with river inputs, winds, waves, tides, and deep-ocean/continental shelf interactions. For instance, transport processes control the fate of river-borne sediments, which in turn affect coastal land loss. Similarly, transport of freshwater, nutrients, and carbon control the dynamics of eutrophication, hypoxia, harmful algal blooms, and coastal acidification. Further, freshwater inflow transports pesticides, herbicides, heavy metals, and oil into receiving estuaries and coastal systems. Lastly, transport processes along the continuum from the rivers and estuaries to coastal and shelf areas and adjacent open ocean (abbreviated herein as “river-estuary-shelf-ocean”) regulate the movements of organisms, including the spatial distributions of individuals and the exchange of genetic information between distinct subpopulations. The Gulf of Mexico Research Initiative (GoMRI) provided unprecedented opportunities to study transport processes along the river-estuary-shelf-ocean continuum in the GoM. The understanding of transport at multiple spatial and temporal scales in this topographically and dynamically complex marginal sea was improved, allowing for more accurate forecasting of the fate of oil and other constituents. For this review, we focus on five specific transport themes: (i) wetland, estuary, and shelf exchanges; (ii) river-estuary coupling; (iii) nearshore and inlet processes; (iv) open ocean transport processes; and (v) river-induced fronts and cross-basin transport. We then discuss the relevancy of GoMRI findings on the transport processes for ecological connectivity and oil transport and fate. We also examine the implications of new findings for informing the response to future oil spills, and the management of coastal resources and ecosystems. Lastly, we summarize the research gaps identified in the many studies and offer recommendations for continuing the momentum of the research provided by the GoMRI effort. A number of uncertainties were identified that occurred in multiple settings. These include the quantification of sediment, carbon, dissolved gasses and nutrient fluxes during storms, consistent specification of the various external forcings used in analyses, methods for smooth integration of multiscale advection mechanisms across different flow regimes, dynamic coupling of the atmosphere with sub-mesoscale and mesoscale phenomena, and methods for simulating finer-scale dynamics over long time periods. Addressing these uncertainties would allow the scientific community to be better prepared to predict the fate of hydrocarbons and their impacts to the coastal ocean, rivers, and marshes in the event of another spill in the GoM.

Download Full-text

Purposefully released tracers

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1988.0051 ◽

1988 ◽

Vol 325 (1583) ◽

pp. 189-200 ◽

Cited By ~ 13

Keyword(s):

Vertical Mixing ◽

Deep Ocean ◽

Experimental Methods ◽

Open Ocean ◽

Sulphur Hexafluoride ◽

Present Generation ◽

Mixing Rates ◽

Exchange Properties ◽

Tracer Experiments ◽

Small Basin

It has been recognized since the late 1970s that it should be possible to use the release of conservative tracers into the deep ocean to measure vertical mixing rates. Diapycnal mixing (i.e. vertical mixing across density strata) is rather crudely described by the present generation of ocean models, usually being taken to be constant irrespective of depth. Model circulations are, however, sensitive to quite minor changes in this assumption. Technology and experimental methods in the open ocean with perfluorinated tracers have now advanced to the state where direct-tracer experiments are feasible and a pilot study in a small basin has given encouraging results. The design of open-ocean experiments is discussed. Consideration of the problem of sampling a streaky distribution leads to the conclusion that the period between release and sampling should be several times the eddy-rotation time. Although any number of tracers could be used for such experiments, sulphur hexafluoride seems to have unique advantages over other candidates: it has been demonstrated to be conservative at least on a timescale of several months, and can be detected with better sensitivity than other possible tracers. Perfluorinated tracers show promise in other areas besides deep-sea oceanography: they are well suited to studies in the coastal ocean and could be used to measure dispersion and air—sea exchange properties at the surface.

Download Full-text

The Role of Oscillating Southern Hemisphere Westerly Winds: Southern Ocean Coastal and Open-Ocean Polynyas

Journal of Climate ◽

10.1175/jcli-d-17-0237.1 ◽

2018 ◽

Vol 31 (3) ◽

pp. 1053-1073 ◽

Cited By ~ 6

Author(s):

Woo Geun Cheon ◽

Chang-Bong Cho ◽

Arnold L. Gordon ◽

Young Ho Kim ◽

Young-Gyu Park

Keyword(s):

Southern Ocean ◽

Sea Ice ◽

Southern Hemisphere ◽

Ross Sea ◽

Deep Ocean ◽

Open Ocean ◽

Weddell Sea ◽

Wind Forcing ◽

Westerly Winds ◽

Southern Hemisphere Westerly Winds

Abstract An oscillation in intensity of the Southern Hemisphere westerly winds is a major characteristic of the southern annular mode. Its impact upon the sea ice–ocean interactions in the Weddell and Ross Seas is investigated by a sea ice–ocean general circulation model coupled to an energy balance model for three temporal scales and two amplitudes of intensity. It is found that the oscillating wind forcing over the Southern Ocean plays a significant role both in regulating coastal polynyas along the Antarctic margins and in triggering open-ocean polynyas. The formation of coastal polynya in the western Weddell and Ross Seas is enhanced with the intensifying winds, resulting in an increase in the salt flux into the ocean via sea ice formation. Under intensifying winds, an instantaneous spinup within the Weddell and Ross Sea cyclonic gyres causes the warm deep water to upwell, triggering open-ocean polynyas with accompanying deep ocean convection. In contrast to coastal polynyas, open-ocean polynyas in the Weddell and Ross Seas respond differently to the wind forcing and are dependent on its period. That is, the Weddell Sea open-ocean polynya occurs earlier and more frequently than the Ross Sea open-ocean polynya and, more importantly, does not occur when the period of oscillation is sufficiently short. The strong stratification of the Ross Sea and the contraction of the Ross gyre due to the southward shift of Antarctic Circumpolar Current fronts provide unfavorable conditions for the Ross Sea open-ocean polynya. The recovery time of deep ocean heat controls the occurrence frequency of the Weddell Sea open-ocean polynya.

Download Full-text

Varying Biological Activity and Wind Stress Affect the DMS Response during the SAGE Iron Enrichment Experiment

Journal of Marine Science and Engineering ◽

10.3390/jmse8040268 ◽

2020 ◽

Vol 8 (4) ◽

pp. 268

Author(s):

Graham Jones ◽

Mike Harvey ◽

Stacey King ◽

Anke Schneider ◽

Simon Wright ◽

...

Keyword(s):

Surface Waters ◽

Biological Response ◽

Phytoplankton Production ◽

Storm Activity ◽

Chl A ◽

Iron Enrichment ◽

The Third ◽

Enrichment Experiments ◽

High Winds ◽

Microzooplankton Grazing

Surface dissolved dimethylsulfide (DMS) and depth-integrated dimethylsulfoniopropionate (DMSP) measurements were made from March to April 2004 during the SOLAS Air–Sea Gas Exchange Experiment (SAGE), a multiple iron enrichment experiment in subantarctic waters SE of New Zealand. During the first two iron enrichments, chl a and DMS production were constrained, but during the third enrichment, large pulses of DMS occurred in the fertilised IN patch, compared with the unfertilised OUT patch. During the third and fourth iron infusions, total chl a concentrations doubled from 0.52 to 1.02 µg/L. Hapto8s and prasinophytes accounted for 50%, and 20%, respectively, of total chl a. The large pulses of DMS during the third iron enrichment occurred during high dissolved DMSP concentrations and wind strength; changes in dinoflagellate, haptophyte, and cyanobacteria biomass; and increased microzooplankton grazing that exerted a top down control on phytoplankton production. A further fourth iron enrichment did cause surface waters to increase in DMS, but the effect was not as great as that recorded in the third enrichment. Differences in the biological response between SAGE and several other iron enrichment experiments were concluded to reflect microzooplankton grazing activities and the microbial loop dominance, resulting from mixing of the MLD during storm activity and high winds during iron enrichment.

Download Full-text