Late Miocene vegetation and palaeoenvironments of the Drygalski Formation, Heard Island, Indian Ocean: evidence from palynology

2005 ◽  
Vol 17 (3) ◽  
pp. 427-442 ◽  
Author(s):  
ELIZABETH M. TRUSWELL ◽  
PATRICK G. QUILTY ◽  
A. MCMINN ◽  
M.K. MACPHAIL ◽  
G.E. WHELLER
Keyword(s):  
Indian Ocean ◽  
Southern Ocean ◽  
Late Miocene ◽  
Tree Species ◽  
Frontal Zone ◽  
Tierra Del Fuego ◽  
Tree Pollen ◽  
Marine Diatoms ◽  
Heard Island ◽  
The Antarctic

Well sorted, fine lithic sandstone within the Drygalski Formation at Cape Lockyer on the southern tip of Heard Island, preserves a diverse terrestrial palynoflora as well as marine diatoms and a few foraminifera. A combination of these elements suggests a Late Miocene age (10–5 Ma). The palaeovegetation was markedly different from that presently on the island, and appears to comprise at least two ecologically distinct communities: open heath or herbfield dominated by grasses and Asteraceae, and a more mesophytic community dominated by ferns but also including lycopods and angiosperms such as Gunnera. This may have represented a coastal flora similar to the ‘fern-bush’ community that exists now on Southern Ocean islands north of the Antarctic Polar Frontal Zone, and in Tierra del Fuego; however, there is no evidence of tree species in the local flora and trace amounts of tree pollen present may have blown in from other landmasses in the region.

scholarly journals Carbonate system in the water masses of the Southeast Atlantic sector of the Southern Ocean during February and March 2008

2011 ◽  
Vol 8 (5) ◽  
pp. 1401-1413 ◽  
Author(s):  
M. González-Dávila ◽  
J. M. Santana-Casiano ◽  
R. A. Fine ◽  
J. Happell ◽  
B. Delille ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Deep Water ◽  
Frontal Zone ◽  
Water Masses ◽  
Total Alkalinity ◽  
Carbonate System ◽  
Aragonite Saturation ◽  
Atlantic Sector ◽  
Circumpolar Deep Water ◽  
The Antarctic

Abstract. Carbonate system variables were measured in the South Atlantic sector of the Southern Ocean along a transect from South Africa to the southern limit of the Antarctic Circumpolar Current (ACC) from February to March 2008. Eddies detached from the retroflection of the Agulhas Current increased the gradients observed along the fronts. Minima in the fugacity of CO2, fCO2, and maxima in pH on either side of the frontal zone were observed, noting that within the frontal zone fCO2 reached maximum values and pH was at a minimum. Vertical distributions of water masses were described by their carbonate system properties and their relationship to CFC concentrations. Upper Circumpolar Deep Water (UCDW) and Lower Circumpolar Deep Water (LCDW) offered pHT,25 values of 7.56 and 7.61, respectively. The UCDW also had higher concentrations of CFC-12 (>0.2 pmol kg−1) as compared to deeper waters, revealing that UCDW was mixed with recently ventilated waters. Calcite and aragonite saturation states (Ω) were also affected by the presence of these two water masses with high carbonate concentrations. The aragonite saturation horizon was observed at 1000 m in the subtropical area and north of the Subantarctic Front. At the position of the Polar Front, and under the influence of UCDW and LCDW, the aragonite saturation horizon deepened from 800 m to 1500 m at 50.37° S, and reached 700 m south of 57.5° S. High latitudes proved to be the most sensitive areas to predicted anthropogenic carbon increase. Buffer coefficients related to changes in [CO2], [H+] and Ω with changes in dissolved inorganic carbon (CT) and total alkalinity (AT) offered minima values in the Antarctic Intermediate Water and UCDW layers. These coefficients suggest that a small increase in CT will sharply decrease the status of pH and carbonate saturation. Here we present data that suggest that south of 55° S, surface water will be under-saturated with respect to aragonite within the next few decades.

scholarly journals X.—On the Deep and Shallow-water Marine Fauna of the Kerguelen Region of the Great Southern Ocean

1897 ◽  
Vol 38 (2) ◽  
pp. 343-500 ◽  
Author(s):  
John Murray
Keyword(s):  
Southern Ocean ◽  
Shallow Water ◽  
Sea Level ◽  
Marine Fauna ◽  
Kerguelen Island ◽  
Cape Of Good Hope ◽  
Heard Island ◽  
The World ◽  
The Antarctic

During her famous circumnavigation of the world, H.M.S. Challenger left the Cape of Good Hope on the 17th December 1873, and, proceeding in a south-easterly direction, visited in succession Prince Edward and Marion Islands, the Crozet Islands, Kerguelen Island, and Heard Island. From Heard Island the Expedition sailed southward, and on the 16th February 1874 passed ten miles beyond the Antarctic Circle in longitude 78° 22′ E., the ship being at this time surrounded by a large number of huge tabular icebergs, some of them four miles in length, and all with perpendicular sides rising about 200 feet above the sea-level. From this most southerly point the Challenger took a north-easterly course towards Melbourne in Australia, where she arrived on the 17th March 1874.

scholarly journals Carbonate system buffering in the water masses of the Southwest Atlantic sector of the Southern Ocean during February–March 2008

2011 ◽  
Vol 8 (1) ◽  
pp. 435-462
Author(s):  
M. González-Dávila ◽  
J. M. Santana-Casiano ◽  
R. A. Fine ◽  
J. Happell ◽  
B. Delille ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Deep Water ◽  
Frontal Zone ◽  
Water Masses ◽  
Intermediate Water ◽  
Carbonate System ◽  
Atlantic Sector ◽  
Circumpolar Deep Water ◽  
The Antarctic

Abstract. Carbonate system variables were measured in the South Atlantic sector of the Southern Ocean along a transect from South Africa to the southern limit of the Antarctic Circumpolar Current (ACC) in February–March 2008. Eddies detach from retroflection of the Agulhas Current located north of the Subantarctic Front (SAF). The eddies increase the gradients observed at the fronts so that minima in fCO2 and maxima in pH in situ on either side of the frontal zone are observed, while within the frontal zone fCO2 reached maximum values and pH in situ was a minimum. Mixing at the frontal zones, in particular where cyclonic rings were located, brought up CO2-rich water (low pH and high nutrient) that spread out the fronts where recent biological production favored by the nutrient input increases the pH in situ and decreases the fCO2 levels. Vertical distributions of water masses were described by their carbonate system properties and their relationship to CFC concentrations. Upper Circumpolar Deep Water (UCDW) and Lower Circumpolar Deep Water (LCDW) had pHT,25 values of 7.56 and 7.61, respectively. UCDW also had higher concentrations of CFC-12 (>0.2 pmol kg−1) as compared to deeper waters, revealing the mixing with recently ventilated waters. Calcite and aragonite saturation states (Ω) were also affected by the presence of these two water masses with high carbonate concentration. Ωarag = 1 was observed at 1000 m in the subtropical area and north of the SAF. At the position of the Polar front and under the influence of UCDW and LCDW Ωarag = 1 deepen from 600 m to 1500 m at 50.37° S, and it reaches to 700 m south of 57.5° S. High latitudes are the most sensitive areas under future anthropogenic carbon increase. Buffer coefficients related to changes in [CO2], [H+] and Ω with changes in CT and AT showed the minimum values are found in the Antarctic Intermediate Water (AAIW), and UCDW layers. These coefficients suggest that a small increase in CT will sharply decrease the pH and the carbonate saturation states. Here we present data that are used to suggest that south of 55° S by the year 2045 surface water will be undersaturated in aragonite.

scholarly journals Spatial Distributions of 226Ra and 228Ra in the Indian and Southern Oceans in 2020 and Their Implications for Unique Currents

2021 ◽  
Author(s):  
Mutsuo Inoue ◽  
Shotaro Hanaki ◽  
Hiroaki Kameyama ◽  
Yuichiro Kumamoto ◽  
Seiya Nagao
Keyword(s):  
Indian Ocean ◽  
Southern Ocean ◽  
Western Indian Ocean ◽  
Polar Front ◽  
Transport Systems ◽  
Material Transport ◽  
Vertical Variations ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Southern Oceans

Abstract We examined the spatial variations in 226Ra and 228Ra concentrations from the surface to a depth of 830 m in the Indian and Southern Oceans during December 2019–January 2020. Notably, 226Ra concentrations at the surface increased sharply from 30°S to 60°S along an ~55°E transect (1.4 to 2.9 mBq/L), exhibiting small vertical variations, while 228Ra became depleted, particularly in the Southern Ocean. These distributions indicated the ocean-scale northward lateral movements of 226Ra-rich and 228Ra-depleted currents originating from the Antarctic Circumpolar Current (ACC). Using 226Ra concentrations, the fractions of the ACC at depths of 0–800 m were estimated to decrease from 0.95 to 0.14 from 60°S to 30°S through 0.56 at 43°S. The fractions in the subantarctic area the western Indian Ocean were higher than those previously reported from the eastern, indicating the preferential transport of the ACC. The fractions obtained were approximately equivalent to those in the western Indian section in the 1970s. This could be attributed to the minimal effects of the southward shift of the polar front due to global warming over the last 40 y, implying no notable changes in soluble material transport systems from the Southern Ocean to southern Indian Ocean.

Australasian Southern Ocean frontal stucture during summer 1976-77

1982 ◽  
Vol 33 (1) ◽  
pp. 3 ◽  
Author(s):  
RJ Edwards ◽  
WJ Emery
Keyword(s):  
Southern Ocean ◽  
Frontal Zone ◽  
Polar Front ◽  
Temperature Structure ◽  
Surface Salinity ◽  
Mode Water ◽  
Polar Frontal Zone ◽  
Eastern Australia ◽  
The Antarctic ◽  
Subantarctic Front

Fourteen north-south expendable bathythermograph temperature sections are used to define the positions of the Subtropical Convergence, the Subantarctic Front and the Polar Front in the Australasian sector of the Southern Ocean. The data were collected by supply vessels sailing to the Antarctic mainland during the austral summer of 1976-77. Frontal features are identified on the basis of both temperature structure and observations of surface salinity. The Polar Front is found to be more convoluted than the other fronts, leading to wide and narrow sections of the Antarctic Polar Frontal Zone between it and the Subantarctic Front. South-west of Australia the Subantarctic Front shifts north along with the Subtropical Convergence, and the Antarctic Polar Frontal Zone is at its widest. East of a southward shift of all three fronts, south of eastern Australia, they separate to give almost equal separations of about 700 km between fronts south-east of New Zealand. The homogeneous Subantarctic Mode Water between the Subantarctic Front and the Subtropical Convergence is found to be progressively warmer towards the west. Though the data is not truly synoptic, being spread over 3½ months, it does reflect the frontal structure during the period of observation.

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