scholarly journals Massive Southern Ocean phytoplankton bloom fed by iron of possible hydrothermal origin

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Casey M. S. Schine ◽  
Anne-Carlijn Alderkamp ◽  
Gert van Dijken ◽  
Loes J. A. Gerringa ◽  
Sara Sergi ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Primary Production ◽  
Hydrothermal Vent ◽  
Hydrothermal Vents ◽  
Phytoplankton Bloom ◽  
Hydrothermal Origin ◽  
The Pacific ◽  
High Nutrient ◽  
Circumpolar Current ◽  
The Antarctic

AbstractPrimary production in the Southern Ocean (SO) is limited by iron availability. Hydrothermal vents have been identified as a potentially important source of iron to SO surface waters. Here we identify a recurring phytoplankton bloom in the high-nutrient, low-chlorophyll waters of the Antarctic Circumpolar Current in the Pacific sector of the SO, that we argue is fed by iron of hydrothermal origin. In January 2014 the bloom covered an area of ~266,000 km2 with depth-integrated chlorophyll a > 300 mg m−2, primary production rates >1 g C m−2 d−1, and a mean CO2 flux of −0.38 g C m−2 d−1. The elevated iron supporting this bloom is likely of hydrothermal origin based on the recurrent position of the bloom relative to two active hydrothermal vent fields along the Australian Antarctic Ridge and the association of the elevated iron with a distinct water mass characteristic of a nonbuoyant hydrothermal vent plume.

scholarly journals Estimating a Submesoscale Diffusivity Using a Roughness Measure Applied to a Tracer Release Experiment in the Southern Ocean

2015 ◽  
Vol 45 (6) ◽  
pp. 1610-1631 ◽  
Author(s):  
Emma J. D. Boland ◽  
Emily Shuckburgh ◽  
Peter H. Haynes ◽  
James R. Ledwell ◽  
Marie-José Messias ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Antarctic Circumpolar Current ◽  
Drake Passage ◽  
Velocity Fields ◽  
Small Scale ◽  
The Pacific ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Mesoscale Processes ◽  
Submesoscale Processes

AbstractThe use of a measure to diagnose submesoscale isopycnal diffusivity by determining the best match between observations of a tracer and simulations with varying small-scale diffusivities is tested. Specifically, the robustness of a “roughness” measure to discriminate between tracer fields experiencing different submesoscale isopycnal diffusivities and advected by scaled altimetric velocity fields is investigated. This measure is used to compare numerical simulations of the tracer released at a depth of about 1.5 km in the Pacific sector of the Southern Ocean during the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) field campaign with observations of the tracer taken on DIMES cruises. The authors find that simulations with an isopycnal diffusivity of ~20 m2 s−1 best match observations in the Pacific sector of the Antarctic Circumpolar Current (ACC), rising to ~20–50 m2 s−1 through Drake Passage, representing submesoscale processes and any mesoscale processes unresolved by the advecting altimetry fields. The roughness measure is demonstrated to be a statistically robust way to estimate a small-scale diffusivity when measurements are relatively sparse in space and time, although it does not work if there are too few measurements overall. The planning of tracer measurements during a cruise in order to maximize the robustness of the roughness measure is also considered. It is found that the robustness is increased if the spatial resolution of tracer measurements is increased with the time since tracer release.

scholarly journals Tracing Southwest Pacific Bottom Water Using Potential Vorticity and Helium-3

2012 ◽  
Vol 42 (12) ◽  
pp. 2153-2168 ◽  
Author(s):  
Stephanie M. Downes ◽  
Robert M. Key ◽  
Alejandro H. Orsi ◽  
Kevin G. Speer ◽  
James H. Swift
Keyword(s):  
Potential Vorticity ◽  
Hydrothermal Vents ◽  
Bottom Water ◽  
Drake Passage ◽  
South Pacific ◽  
The South ◽  
Southwest Pacific ◽  
The Pacific ◽  
Circumpolar Current ◽  
The Antarctic

Abstract This study uses potential vorticity and other tracers to identify the pathways of the densest form of Circumpolar Deep Water in the South Pacific, termed “Southwest Pacific Bottom Water” (SPBW), along the 28.2 kg m−3 surface. This study focuses on the potential vorticity signals associated with three major dynamical processes occurring in the vicinity of the Pacific–Antarctic Ridge: 1) the strong flow of the Antarctic Circumpolar Current (ACC), 2) lateral eddy stirring, and 3) heat and stratification changes in bottom waters induced by hydrothermal vents. These processes result in southward and downstream advection of low potential vorticity along rising isopycnal surfaces. Using δ3He released from the hydrothermal vents, the influence of volcanic activity on the SPBW may be traced across the South Pacific along the path of the ACC to Drake Passage. SPBW also flows within the southern limb of the Ross Gyre, reaching the Antarctic Slope in places and contributes via entrainment to the formation of Antarctic Bottom Water. Finally, it is shown that the magnitude and location of the potential vorticity signals associated with SPBW have endured over at least the last two decades, and that they are unique to the South Pacific sector.

scholarly journals Topographic Control of Southern Ocean Gyres and the Antarctic Circumpolar Current: A Barotropic Perspective

2019 ◽  
Vol 49 (12) ◽  
pp. 3221-3244 ◽  
Author(s):  
Ryan D. Patmore ◽  
Paul R. Holland ◽  
David R. Munday ◽  
Alberto C. Naveira Garabato ◽  
David P. Stevens ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Antarctic Circumpolar Current ◽  
Large Scale ◽  
Volume Transport ◽  
Topographic Features ◽  
Conservation Of Momentum ◽  
Ridge Width ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Ridge Geometry

AbstractIn the Southern Ocean the Antarctic Circumpolar Current is significantly steered by large topographic features, and subpolar gyres form in their lee. The geometry of topographic features in the Southern Ocean is highly variable, but the influence of this variation on the large-scale flow is poorly understood. Using idealized barotropic simulations of a zonal channel with a meridional ridge, it is found that the ridge geometry is important for determining the net zonal volume transport. A relationship is observed between ridge width and volume transport that is determined by the form stress generated by the ridge. Gyre formation is also highly reliant on the ridge geometry. A steep ridge allows gyres to form within regions of unblocked geostrophic (f/H) contours, with an increase in gyre strength as the ridge width is reduced. These relationships among ridge width, gyre strength, and net zonal volume transport emerge to simultaneously satisfy the conservation of momentum and vorticity.

scholarly journals Coupling Influences of ENSO and PDO on the Inter-Decadal SST Variability of the ACC around the Western South Atlantic

2019 ◽  
Vol 11 (18) ◽  
pp. 4853
Author(s):  
You-Lin Wang ◽  
Yu-Chen Hsu ◽  
Chung-Pan Lee ◽  
Chau-Ron Wu
Keyword(s):  
Antarctic Circumpolar Current ◽  
Water Mass ◽  
Southern Oscillation ◽  
Drake Passage ◽  
South Atlantic ◽  
Sst Variability ◽  
The Pacific ◽  
Circumpolar Current ◽  
The Antarctic

The Antarctic Circumpolar Current (ACC) plays an important role in the climate as it balances heat energy and water mass between the Pacific and Atlantic Oceans through the Drake Passage. However, because the historical measurements and observations are extremely limited, the decadal and long-term variations of the ACC around the western South Atlantic Ocean are rarely studied. By analyzing reconstructed sea surface temperatures (SSTs) in a 147-year period (1870–2016), previous studies have shown that SST anomalies (SSTAs) around the Antarctic Peninsula and South America had the same phase change as the El Niño Southern Oscillation (ENSO). This study further showed that changes in SSTAs in the regions mentioned above were enlarged when the Pacific Decadal Oscillation (PDO) and the ENSO were in the same warm or cold phase, implying that changes in the SST of higher latitude oceans could be enhanced when the influence of the ENSO is considered along with the PDO.

scholarly journals Coccolithophore populations and their contribution to carbonate export during an annual cycle in the Australian sector of the Antarctic zone

2018 ◽  
Vol 15 (6) ◽  
pp. 1843-1862 ◽  
Author(s):  
Andrés S. Rigual Hernández ◽  
José A. Flores ◽  
Francisco J. Sierro ◽  
Miguel A. Fuertes ◽  
Lluïsa Cros ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Ocean Acidification ◽  
Deep Ocean ◽  
Sediment Traps ◽  
Global Ocean ◽  
Field Observations ◽  
Scotia Sea ◽  
Allochthonous Species ◽  
Circumpolar Current ◽  
The Antarctic

Abstract. The Southern Ocean is experiencing rapid and relentless change in its physical and biogeochemical properties. The rate of warming of the Antarctic Circumpolar Current exceeds that of the global ocean, and the enhanced uptake of carbon dioxide is causing basin-wide ocean acidification. Observational data suggest that these changes are influencing the distribution and composition of pelagic plankton communities. Long-term and annual field observations on key environmental variables and organisms are a critical basis for predicting changes in Southern Ocean ecosystems. These observations are particularly needed, since high-latitude systems have been projected to experience the most severe impacts of ocean acidification and invasions of allochthonous species. Coccolithophores are the most prolific calcium-carbonate-producing phytoplankton group playing an important role in Southern Ocean biogeochemical cycles. Satellite imagery has revealed elevated particulate inorganic carbon concentrations near the major circumpolar fronts of the Southern Ocean that can be attributed to the coccolithophore Emiliania huxleyi. Recent studies have suggested changes during the last decades in the distribution and abundance of Southern Ocean coccolithophores. However, due to limited field observations, the distribution, diversity and state of coccolithophore populations in the Southern Ocean remain poorly characterised. We report here on seasonal variations in the abundance and composition of coccolithophore assemblages collected by two moored sediment traps deployed at the Antarctic zone south of Australia (2000 and 3700 m of depth) for 1 year in 2001–2002. Additionally, seasonal changes in coccolith weights of E. huxleyi populations were estimated using circularly polarised micrographs analysed with C-Calcita software. Our findings indicate that (1) coccolithophore sinking assemblages were nearly monospecific for E. huxleyi morphotype B/C in the Antarctic zone waters in 2001–2002; (2) coccoliths captured by the traps experienced weight and length reduction during summer (December–February); (3) the estimated annual coccolith weight of E. huxleyi at both sediment traps (2.11 ± 0.96 and 2.13 ± 0.91 pg at 2000 and 3700 m) was consistent with previous studies for morphotype B/C in other Southern Ocean settings (Scotia Sea and Patagonian shelf); and (4) coccolithophores accounted for approximately 2–5 % of the annual deep-ocean CaCO3 flux. Our results are the first annual record of coccolithophore abundance, composition and degree of calcification in the Antarctic zone. They provide a baseline against which to monitor coccolithophore responses to changes in the environmental conditions expected for this region in coming decades.

scholarly journals Detecting and Characterizing Ekman Currents in the Southern Ocean

2015 ◽  
Vol 45 (5) ◽  
pp. 1205-1223 ◽  
Author(s):  
Christopher J. Roach ◽  
Helen E. Phillips ◽  
Nathaniel L. Bindoff ◽  
Stephen R. Rintoul
Keyword(s):  
Southern Ocean ◽  
Classical Theory ◽  
Geographical Area ◽  
Drake Passage ◽  
Current Decay ◽  
Common Value ◽  
Constant Viscosity ◽  
Circumpolar Current ◽  
Reasonable Description ◽  
The Antarctic

AbstractThis study presents a unique array of velocity profiles from Electromagnetic Autonomous Profiling Explorer (EM-APEX) profiling floats in the Antarctic Circumpolar Current (ACC) north of Kerguelen. The authors use these profiles to examine the nature of Ekman spirals, formed by the action of the wind on the ocean’s surface, in light of Ekman’s classical linear theory and more recent enhancements. Vertical decay scales of the Ekman spirals were estimated independently from current amplitude and rotation. Assuming a vertically uniform geostrophic current, decay scales from the Ekman current heading were twice as large as those from the current speed decay, indicating a compressed spiral, consistent with prior observations and violating the classical theory. However, if geostrophic shear is accurately removed, the observed Ekman spiral is as predicted by classical theory and decay scales estimated from amplitude decay and rotation converge toward a common value. No statistically robust relationship is found between stratification and Ekman decay scales. The results indicate that compressed spirals observed in the Southern Ocean arise from aliasing of depth-varying geostrophic currents into the Ekman spiral, as opposed to surface trapping of Ekman currents associated with stratification, and extends the geographical area of similar results from Drake Passage (Polton et al. 2013). Accounting for this effect, the authors find that constant viscosity Ekman models offer a reasonable description of momentum mixing into the upper ocean in the ACC north of Kerguelen. These results demonstrate the effectiveness of a new method and provide additional evidence that the same processes are active for the entire Southern Ocean.

scholarly journals Estimating the Four-Dimensional Structure of the Southern Ocean Using Satellite Altimetry

2011 ◽  
Vol 28 (4) ◽  
pp. 548-568 ◽  
Author(s):  
A. J. S. Meijers ◽  
N. L. Bindoff ◽  
S. R. Rintoul
Keyword(s):  
Southern Ocean ◽  
Satellite Altimetry ◽  
Velocity Structure ◽  
Velocity Fields ◽  
Optimal Interpolation ◽  
Dimensional Structure ◽  
Strongly Correlated ◽  
Circumpolar Current ◽  
The Antarctic

Abstract A gravest empirical mode (GEM) projection of temperature and salinity fields over the circumpolar Southern Ocean is presented and is used in combination with satellite altimetry to produce gridded, full-depth, time-evolving temperature, salinity, and velocity fields. Optimal interpolation of historical hydrography, including Argo floats, is used to produce GEM projections of the circumpolar temperature and salinity fields. Parameterizing these fields by dynamic height allows the use of altimetric SSH values from 1992–2006 to create synoptic temperature and salinity fields at weekly intervals on a ⅓° grid at 36 depth levels. The satellite-derived temperature and salinity fields generally capture over 90% of the property variance below the thermocline, with RMS residuals of 1.16°C and 0.132 in salinity at the surface, decreasing to less than 0.45°C and 0.05 below 500 dbar. The combination of altimetry with the GEM fields allows the resolution of the subsurface structure of the filamentary fronts and eddy features. Velocity fields derived from the time-evolving temperature and salinity fields reproduce the Antarctic Circumpolar Current (ACC) velocity structure well, and are strongly correlated (r > 0.7) with in situ measurements from current meters and drifters, with RMS velocity residuals of 4.8–14.8 cm−1 in the Subantarctic Front.

Sign in / Sign up

Export Citation Format

Share Document