| 1. |
|
|
| 2. |
- Boyd, Philip W., et al.
(författare)
-
The role of biota in the Southern Ocean carbon cycle
- 2024
-
Ingår i: NATURE REVIEWS EARTH & ENVIRONMENT. - 2662-138X. ; 5:5, s. 390-408
-
Forskningsöversikt (refereegranskat)abstract
- The Southern Ocean, although relatively understudied owing to its harsh environment and geographical isolation, has been shown to contribute substantially to processes that drive the global carbon cycle. For example, phytoplankton photosynthesis transforms carbon dioxide into new particles and dissolved organic carbon. The magnitude of these transformations depends on the unique oceanographic and biogeochemical properties of the Southern Ocean. In this Review, we synthesize observations of biologically mediated carbon flows derived from the expanded observational network provided by remote-sensing and autonomous platforms. These observations reveal patterns in the magnitude of net primary production, including under-ice blooms and subsurface chlorophyll maxima. Basin-scale annual estimates of the planktonic contribution to the Southern Ocean carbon cycle can also be calculated, indicating that the export of biogenic particles and dissolved organic carbon to depth accounts for 20-30% (around 3 Gt yr-1) of the global export flux. This flux partially compensates for carbon dioxide outgassing following upwelling, making the Southern Ocean a 0.4-0.7 Gt C yr-1 sink. This export flux is surprisingly large given that phytoplankton are iron-limited with low productivity in more than 80% of the Southern Ocean. Solving such enigmas will require the development of four-dimensional regional observatories and the use of data-assimilation and machine-learning techniques to integrate datasets. The Southern Ocean represents a substantial carbon sink and heavily influences global carbon fluxes. This Review describes how an expanding suite of observations are providing increasing insight into the contribution of biota and plankton to the carbon cycle in the Southern Ocean. Increasing coverage from a suite of observations from autonomous platforms will reduce uncertainties on estimates of key processes in the regional carbon cycle that determine the magnitude of the Southern Ocean carbon sink.Episodic storms enhance chlorophyll stocks, presumably owing to enhanced iron supply from depth, but also drive concurrent carbon dioxide outgassing, with unknown cumulative effects on the regional carbon cycle.The influence of climate change on the Southern Ocean and Antarctica is expected to alter the partitioning of basin-scale net primary production between open water, sea ice and under ice.Observations from profiling robotic floats are providing important insights into how the fate of phytoplankton carbon drives regional patterns in export flux in the ocean's interior over multiple annual cycles.The inability to remotely measure dissolved iron or dissolved organic carbon concentrations makes it difficult to understand pivotal processes in the Southern Ocean carbon cycle.Models using data assimilation are already providing promising guidelines on how to deploy autonomous platforms to address key questions around the regional carbon cycle.
|
|
| 3. |
- Torstensson, Anders, et al.
(författare)
-
Sea-ice microbial communities in the Central Arctic Ocean : Limited responses to short-term pCO(2) perturbations
- 2021
-
Ingår i: Limnology and Oceanography. - : John Wiley & Sons. - 0024-3590 .- 1939-5590. ; 66, s. S383-S400
-
Tidskriftsartikel (refereegranskat)abstract
- The Arctic Ocean is more susceptible to ocean acidification than other marine environments due to its weaker buffering capacity, while its cold surface water with relatively low salinity promotes atmospheric CO2 uptake. We studied how sea-ice microbial communities in the central Arctic Ocean may be affected by changes in the carbonate system expected as a consequence of ocean acidification. In a series of four experiments during late summer 2018 aboard the icebreaker Oden, we addressed microbial growth, production of dissolved organic carbon (DOC) and extracellular polymeric substances (EPS), photosynthetic activity, and bacterial assemblage structure as sea-ice microbial communities were exposed to elevated partial pressures of CO2 (pCO(2)). We incubated intact, bottom ice-core sections and dislodged, under-ice algal aggregates (dominated by Melosira arctica) in separate experiments under approximately 400, 650, 1000, and 2000 mu atm pCO(2) for 10 d under different nutrient regimes. The results indicate that the growth of sea-ice algae and bacteria was unaffected by these higher pCO(2) levels, and concentrations of DOC and EPS were unaffected by a shifted inorganic C/N balance, resulting from the CO2 enrichment. These central Arctic sea-ice microbial communities thus appear to be largely insensitive to short-term pCO(2) perturbations. Given the natural, seasonally driven fluctuations in the carbonate system of sea ice, its resident microorganisms may be sufficiently tolerant of large variations in pCO(2) and thus less vulnerable than pelagic communities to the impacts of ocean acidification, increasing the ecological importance of sea-ice microorganisms even as the loss of Arctic sea ice continues.
|
|
