Mesoscale features and phytoplankton biomass at the GoodHope line in the Southern Ocean during austral summer

Swart, Sebastiaan; Thomalla, S.; Monteiro, Pms; Ansorge, I. J.

doi:10.2989/1814232x.2012.749811

Cited by 9 publications

(10 citation statements)

References 68 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The assimilation signal as a summer remnant is supported by a simple mixing calculation which indicates that the deep‐to‐surface [NO 3 − ] decrease in the wintertime AZ is driven primarily by the low [NO 3 − ] of the summer mixed layer, the incorporation of which into the winter mixed layer effectively dilutes its concentration. For the summertime AZ, we use a mixed layer depth of 75 m [ Joubert et al ., ; Thomalla et al ., ; Swart et al ., ] and a [NO 3 − ] of 24 µM, which routine summer sampling shows to be representative of the region (Thomalla et al, unpublished data, 2008–2014; Fawcett et al, unpublished data, 2014). Deepening a summer mixed layer with these properties to 116 m (the average AZ mixed layer depth observed during the winter cruise) by mixing with underlying UCDW (with a [NO 3 − ] of 33.5 µM) would yield a winter mixed layer with a [NO 3 − ] of 27.4 µM; this prediction is very close to the observed average [NO 3 − ] of 27.3 µM for the wintertime AZ mixed layer.…”

Section: Discussionmentioning

confidence: 99%

“…To provide a quantitative estimate for the required δ 15 N of newly nitrified nitrate, we consider the AZ winter mixed layer to have four different nitrate sources: (1) the previous summer mixed layer in this region, with a δ 15 N of 6.3‰ and [NO 3 − ] of 24.1 µM (Fawcett et al, unpublished data, 2014) and a thickness of 75 m [ Joubert et al ., ; Thomalla et al ., ; Swart et al ., ]; (2) the previous summer T min , with a δ 15 N of 5.4‰ and [NO 3 − ] of 27.3 µM (using our average AZ winter mixed layer properties as a proxy) and a thickness of 41 m (taken from the difference between average winter and summer mixed layer depths); (3) newly nitrified nitrate, assuming complete regeneration of the summertime AZ suspended PN pool, with an average [PN] of 1.3 µM (Fawcett et al, unpublished data, 2014); and (4) UCDW, with a δ 15 N of 4.8‰ and [NO 3 − ] of 33.5 µM. In principle, in order to reproduce the average observed properties of the AZ winter mixed layer (δ 15 N of 5.4‰ and [NO 3 − ] of 27.3 µM) from this combination of sources, UCDW would need to contribute 0.8 µM of nitrate through upwelling and vertical mixing between summer and winter sampling.…”

Section: Discussionmentioning

confidence: 99%

Section: Summer-to-autumn Decline In Suspended Pn δ 15 Nmentioning

confidence: 99%

See 2 more Smart Citations

Isotopic evidence for nitrification in the Antarctic winter mixed layer

Smart

Fawcett

Thomalla

et al. 2015

Global Biogeochemical Cycles

View full text Add to dashboard Cite

We report wintertime nitrogen and oxygen isotope ratios (δ 15 N and δ 18 O) of seawater nitrate in the Southern Ocean south of Africa. Depth profile and underway surface samples collected in July 2012 extend from the subtropics to just beyond the Antarctic winter sea ice edge. We focus here on the Antarctic region (south of 50.3°S), where application of the Rayleigh model to depth profile δ 15 N data yields estimates for the isotope effect (the degree of isotope discrimination) of nitrate assimilation (1.6-3.3‰) that are significantly lower than commonly observed in the summertime Antarctic (5-8‰). The δ 18 O data from the same depth profiles and lateral δ 15 N variations within the mixed layer, however, imply O and N isotope effects that are more similar to those suggested by summertime data. These findings point to active nitrification (i.e., regeneration of organic matter to nitrate) within the Antarctic winter mixed layer. Nitrite removal from samples reveals a low δ 15 N for nitrite in the winter mixed layer (À40‰ to À20‰), consistent with nitrification, but does not remove the observation of an anomalously low δ 15 N for nitrate. The winter data, and the nitrification they reveal, explain the previous observation of an anomalously low δ 15 N for nitrate in the temperature minimum layer (remnant winter mixed layer) of summertime depth profiles. At the same time, the wintertime data require a low δ 15 N for the combined organic N and ammonium in the autumn mixed layer that is available for wintertime nitrification, pointing to intense N recycling as a pervasive condition of the Antarctic in late summer.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Summer-to-autumn Decline In Suspended Pn δ 15 Nmentioning

confidence: 99%

See 1 more Smart Citation

Isotopic evidence for nitrification in the Antarctic winter mixed layer

Smart

Fawcett

Thomalla

et al. 2015

Global Biogeochemical Cycles

View full text Add to dashboard Cite

show abstract

“…2a). The patches of high chlorophyll concentrations may be related to the opening of polynyas in the sea ice and relieving of light limitation Swart et al, 2012;Planquette et al, 2013). High chlorophyll concentrations are observed in places along the Antarctic coastline and upon the Antarctic shelf.…”

Section: Chlorophyll Concentrations Near the Antarctic Coastlinementioning

confidence: 99%

Inferring source regions and supply mechanisms of iron in the Southern Ocean from satellite chlorophyll data

Graham

Boer

Sebille

et al. 2015

Deep Sea Research Part I: Oceanographic Research Papers

View full text Add to dashboard Cite

Keywords: chlorophyll shelf sediments upwelling ocean fronts sea surface height dust glacial-interglacial cycles a b s t r a c t Primary productivity is limited by the availability of iron over large areas of the global ocean. Changes in the supply of iron to these regions could have major impacts on primary productivity and the carbon cycle. However, source regions and supply mechanisms of iron to the global oceans remain poorly constrained. Shelf sediments are considered one of the largest sources of dissolved iron to the global ocean, and a large shelf sediment iron flux is prescribed in many biogeochemical models over all areas of bathymetry shallower than 1000 m. Here, we infer the likely location of shelf sediment iron sources in the Southern Ocean, by identifying where satellite chlorophyll concentrations are enhanced over shallow bathymetry ( o1000 m). We further compare chlorophyll concentrations with the position of ocean fronts, to assess the relative role of horizontal advection and upwelling for supplying iron to the ocean surface. We show that mean annual chlorophyll concentrations are not visibly enhanced over areas of shallow bathymetry that are located more than 500 km from a coastline. Mean annual chlorophyll concentrations 4 2 mg m À 3 are only found within 50 km of a continental or island coastline. These results suggest that sedimentary iron sources only exist on continental and island shelves. Large sedimentary iron fluxes do not seem present on seamounts and submerged plateaus. Large chlorophyll blooms develop where the western boundary currents detach from the continental shelves, and turn eastward into the Sub-Antarctic Zone. Chlorophyll concentrations are enhanced along contours of sea surface height extending off the continental shelves, as shown by the trajectories of virtual water parcels in satellite altimetry data. These analyses support the hypothesis that bioavailable iron from continental shelves is entrained into western boundary currents, and advected into the Sub-Antarctic Zone along the Dynamical Subtropical Front. Our results indicate that upwelling at fronts in the open ocean is unlikely to deliver iron to the ocean surface from deep sources. Finally, we hypothesise how a reduction in sea level may have altered the distribution of shelf sediment iron sources in the Southern Ocean and increased export production over the Sub-Antarctic Zone during glacial intervals.

show abstract

“…The "mesoscale" dynamics and associated "submesoscale" features are important contributors to the ocean state and are of crucial importance for biogeochemical and biological processes in the ocean. Gliders offer a new highresolution lens for observing the full seasonal cycle, a dominant mode of the earth system, in their ability to observe the physicalbiological coupling at sub-seasonal and sub-mesoscale (Martin et al, 2009;Swart et al, 2012Swart et al, , 2015Monteiro et al, 2015;Thomalla et al, 2015;Du Plessis et al, 2017).…”

Section: Mesoscale and Submesoscale Phenomenamentioning

confidence: 99%

OceanGliders: A Component of the Integrated GOOS

et al. 2019

View full text Add to dashboard Cite

The OceanGliders program started in 2016 to support active coordination and enhancement of global glider activity. OceanGliders contributes to the international efforts of the Global Ocean Observation System (GOOS) for Climate, Ocean Health, and Operational Services. It brings together marine scientists and engineers operating gliders around the world: (1) to observe the long-term physical, biogeochemical, and biological ocean processes and phenomena that are relevant for societal applications; and, (2) to contribute to the GOOS through real-time and delayed mode data dissemination. The OceanGliders program is distributed across national and regional observing systems and significantly contributes to integrated, multi-scale and multi-platform sampling strategies. OceanGliders shares best practices, requirements, and scientific knowledge needed for glider operations, data collection and analysis. It also monitors global glider activity and supports the dissemination of glider data through regional and global databases, in realtime and delayed modes, facilitating data access to the wider community. OceanGliders currently supports national, regional and global initiatives to maintain and expand the capabilities and application of gliders to meet key global challenges such as improved measurement of ocean boundary currents, water transformation and storm forecast.

show abstract

Mesoscale features and phytoplankton biomass at the GoodHope line in the Southern Ocean during austral summer

Cited by 9 publications

References 68 publications

Isotopic evidence for nitrification in the Antarctic winter mixed layer

Isotopic evidence for nitrification in the Antarctic winter mixed layer

Inferring source regions and supply mechanisms of iron in the Southern Ocean from satellite chlorophyll data

OceanGliders: A Component of the Integrated GOOS

Contact Info

Product

Resources

About