| 1. |
- Maxwell, Tania L., et al.
(författare)
-
Global dataset of soil organic carbon in tidal marshes
- 2023
-
Ingår i: Scientific Data. - : Springer Nature. - 2052-4463. ; 10:1
-
Tidskriftsartikel (refereegranskat)abstract
- Tidal marshes store large amounts of organic carbon in their soils. Field data quantifying soil organic carbon (SOC) stocks provide an important resource for researchers, natural resource managers, and policy-makers working towards the protection, restoration, and valuation of these ecosystems. We collated a global dataset of tidal marsh soil organic carbon (MarSOC) from 99 studies that includes location, soil depth, site name, dry bulk density, SOC, and/or soil organic matter (SOM). The MarSOC dataset includes 17,454 data points from 2,329 unique locations, and 29 countries. We generated a general transfer function for the conversion of SOM to SOC. Using this data we estimated a median (± median absolute deviation) value of 79.2 ± 38.1 Mg SOC ha−1 in the top 30 cm and 231 ± 134 Mg SOC ha−1 in the top 1 m of tidal marsh soils globally. This data can serve as a basis for future work, and may contribute to incorporation of tidal marsh ecosystems into climate change mitigation and adaptation strategies and policies.
|
|
| 2. |
- de Boer, Agatha M., et al.
(författare)
-
The control of the Southern Hemisphere Westerlies on the position of the Subtropical Front
- 2013
-
Ingår i: Journal of Geophysical Research - Oceans. - : American Geophysical Union (AGU). - 2169-9275 .- 2169-9291. ; 118:10, s. 5669-5675
-
Tidskriftsartikel (refereegranskat)abstract
- In recent years the latitudinal position of the Subtropical Front (STF) has emerged as a key parameter in the global climate. A poleward positioned front is thought to allow a greater salt flux from the Indian to the Atlantic Ocean and so drive a stronger Atlantic Meridional Overturning Circulation. Here the common view that the STF aligns with the zero wind stress curl (WSC) is challenged. Based on the STF climatologies of Orsi et al. (1995), Belkin and Gordon (1996), Graham and De Boer (2013), and on satellite scatterometry winds, we find that the zero WSC contour lies on average ∼10°, ∼8°, and ∼5° poleward of the front for the three climatologies, respectively. The circulation in the region between the Subtropical Gyres and the zero WSC contour is not forced by the WSC but rather by the strong bottom pressure torque that is a result of the interaction of the Antarctic Circumpolar Current with the ocean floor topography. The actual control of the position of the STF is crucially dependent on whether the front is regarded as simply a surface water mass boundary or a dynamical front. For the Agulhas Leakage problem, the southern boundary of the so-called Super Gyre may be the most relevant property but this cannot easily be identified in observations.
|
|
| 3. |
- Graham, Robert M., et al.
(författare)
-
Identifying sources and transport pathways of iron in the Southern Ocean
-
Ingår i: Deep Sea Research Part I. - 0967-0637 .- 1879-0119.
-
Tidskriftsartikel (refereegranskat)abstract
- Over large regions of the global ocean primary productivity is limited by the availability of dissolved iron. Changes in the supply of iron to these regions could have major impacts on primary productivity and the carbon cycle. One of the largest sources of dissolved iron to the ocean is thought to be from shelf sediments, and this source is often parameterized in biogeochemical models as a depth dependent iron flux through the seafloor. Using the knowledge that Southern Ocean surface waters are iron limited, we infer source regions of iron to the Southern Ocean by identifying where the most intense chlorophyll blooms develop. We further derive surface current patterns from satellite sea surface height fields to assess the role of the ocean circulation in transporting iron away from these source regions. We find a tight relationship between satellite chlorophyll concentrations and sea surface height. Large chlorophyll blooms develop on the shelf and where the western boundary currents detach from the continental shelves and turn eastward into the Southern Ocean. This is likely due to shelf supplied iron becoming entrained into western boundary currents and advected into the Southern Ocean along the Dynamical Subtropical Front. The most intense chlorophyll blooms are located along coastal margins of islands and continents. Blooms do not develop over submerged seamounts or plateaus in the open ocean. This suggests that shelf sediments in coastal regions act as large bioavailable iron sources to the Southern Ocean. We recommend that a more accurate method of parameterizing the shelf sediment iron flux could be to prescribe this flux only through grid cells neighboring coastlines. Finally, we hypothesize how changes in sea level during glacial-interglacial cycles may have altered the distribution of shelf sediment iron sources in the Southern Ocean and helped to drive export production anomalies in the Sub-Antarctic Zone.
|
|
| 4. |
- Graham, Robert M., et al.
(författare)
-
Inferring source regions and supply mechanisms of iron in the Southern Ocean from satellite chlorophyll data
- 2015
-
Ingår i: Deep Sea Research Part I. - : Elsevier BV. - 0967-0637 .- 1879-0119. ; 104, s. 9-25
-
Tidskriftsartikel (refereegranskat)abstract
- 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 (< 1000 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 > 2 mg m(-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.
|
|
| 5. |
- Sime, Louise C., et al.
(författare)
-
Southern Hemisphere westerly wind changes during the Last Glacial Maximum : model-data comparison
- 2013
-
Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 64, s. 104-120
-
Tidskriftsartikel (refereegranskat)abstract
- The Southern Hemisphere (SH) westerly winds are thought to be critical to global ocean circulation, productivity, and carbon storage. For example, an equatorward shift in the winds, though its affect on the Southern Ocean circulation, has been suggested as the leading cause for the reduction in atmospheric CO2 during the Last Glacial period. Despite the importance of the winds, it is currently not clear, from observations or model results, how they behave during the Last Glacial. Here, an atmospheric modelling study is performed to help determine likely changes in the SH westerly winds during the Last Glacial Maximum (LGM). Using LGM boundary conditions, the maximum in SH westerlies is strengthened by similar to+1 m s(-1) and moved southward by similar to 2 degrees at the 850 hPa pressure level. Boundary layer stabilisation effects over equatorward extended LGM sea-ice can lead to a small apparent equatorward shift in the wind band at the surface. Further sensitivity analysis with individual boundary condition changes indicate that changes in sea surface temperatures are the strongest factor behind the wind change. The HadAM3 atmospheric simulations, along with published PMIP2 coupled climate model simulations, are then assessed against the newly synthesised database of moisture observations for the LGM. Although the moisture data is the most commonly cited evidence in support of a large equatorward shift in the SH winds during the LGM, none of the models that produce realistic LGM precipitation changes show such a large equatorward shift. In fact, the model which best simulates the moisture proxy data is the HadAM3 LGM simulation which shows a small poleward wind shift. While we cannot prove here that a large equatorward shift would not be able to reproduce the moisture data as well, we show that the moisture proxies do not provide an observational evidence base for it.
|
|
