scholarly journals Spatial patterns and key drivers of zooplankton in the north central Indian Ocean

2021 ◽  
pp. 1-19
Author(s):  
H.B.U.G.M. Wimalasiri ◽  
W.R.W.M.A.P. Weerakoon ◽  
R.P.P.K. Jayasinghe ◽  
P. Dalpadado
Keyword(s):  
Indian Ocean ◽  
Spatial Patterns ◽  
North Central ◽  
The North ◽  
Central Indian Ocean ◽  
Key Drivers

scholarly journals Multiple pygmy blue whale acoustic populations in the Indian Ocean: whale song identifies a possible new population

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Emmanuelle C. Leroy ◽  
Jean-Yves Royer ◽  
Abigail Alling ◽  
Ben Maslen ◽  
Tracey L. Rogers
Keyword(s):  
Indian Ocean ◽  
Southern Hemisphere ◽  
Tropical Indian Ocean ◽  
Blue Whale ◽  
The North ◽  
Central Indian Ocean ◽  
Commercial Whaling ◽  
The Indian Ocean ◽  
And Migration ◽  
Blue Whales

AbstractBlue whales were brought to the edge of extinction by commercial whaling in the twentieth century and their recovery rate in the Southern Hemisphere has been slow; they remain endangered. Blue whales, although the largest animals on Earth, are difficult to study in the Southern Hemisphere, thus their population structure, distribution and migration remain poorly known. Fortunately, blue whales produce powerful and stereotyped songs, which prove an effective clue for monitoring their different ‘acoustic populations.’ The DGD-Chagos song has been previously reported in the central Indian Ocean. A comparison of this song with the pygmy blue and Omura’s whale songs shows that the Chagos song are likely produced by a distinct previously unknown pygmy blue whale population. These songs are a large part of the underwater soundscape in the tropical Indian Ocean and have been so for nearly two decades. Seasonal differences in song detections among our six recording sites suggest that the Chagos whales migrate from the eastern to western central Indian Ocean, around the Chagos Archipelago, then further east, up to the north of Western Australia, and possibly further north, as far as Sri Lanka. The Indian Ocean holds a greater diversity of blue whale populations than thought previously.

Evolution, Properties, and Spatial Variability of MJO Convection near and off the Equator during DYNAMO

2015 ◽  
Vol 72 (11) ◽  
pp. 4126-4147 ◽  
Author(s):  
Weixin Xu ◽  
Steven A. Rutledge ◽  
Courtney Schumacher ◽  
Masaki Katsumata
Keyword(s):  
Life Cycle ◽  
Indian Ocean ◽  
Spatial Variability ◽  
Deep Convection ◽  
Equatorial Indian Ocean ◽  
Zonal Winds ◽  
The North ◽  
Central Indian Ocean ◽  
Research And Teaching ◽  
Strong Upward Motion

Abstract This study investigates the evolution, structure, and spatial variability of Madden–Julian oscillation (MJO) convection observed during the 2011/12 Dynamics of the MJO (DYNAMO) field campaign. Generally, the C-band radars located in the near-equatorial Indian Ocean—Shared Mobile Atmospheric Research and Teaching Radar (SMART-R) on Addu Atoll (Gan) and NASA TOGA on the R/V Roger Revelle (Revelle)—observed similar trends in echo-top heights, stratiform rain fraction, and precipitation feature size across the MJO life cycle. These trends are closely related to changes in mid- to upper-tropospheric moisture, sea surface temperature (SST), zonal wind, and diagnosed vertical air motions. However, the evolution of convection, moisture, and vertical air motion at the R/V Mirai (Mirai), located in the intertropical convergence zone (ITCZ) at 8°S, exhibited a pattern nearly opposite to Gan and Revelle. When the MJO was active over the equator, convection was suppressed around Mirai owing to induced subsidence by the strong upward motion to the north. SST and zonal winds near Mirai were nearly invariant across the MJO life cycle, indicating little influence from the MJO in these fields. Compared to Gan and Revelle, Mirai had a significant amount of precipitation that fell from shallow and isolated convection. There were subtle differences in the evolution and properties of the convection observed between Gan and Revelle. Deep convection occurred slightly earlier at Gan compared to Revelle, consistent with the west-to-east progression of the MJO in the central Indian Ocean. Furthermore, convective deepening was more gradual over Revelle compared to Gan, especially during the October MJO event.

A Major Ecosystem Shift in Coastal East African Waters during the 1997/98 Super El Niño as Detected Using Remote Sensing Data

2021 ◽  
Author(s):  
Zoe Jacobs ◽  
Fatma Jebri ◽  
Meric Srokosz ◽  
Dionysios Raitsos ◽  
Stuart Painter ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Indian Ocean ◽  
Remote Sensing Data ◽  
Temporary Increase ◽  
Wind Stress Curl ◽  
Indian Ocean Dipole Event ◽  
The North ◽  
Positive Indian Ocean Dipole ◽  
Central Indian Ocean ◽  
The Impact

<p>Under the impact of natural and anthropogenic climate variability, upwelling systems are known to change their properties leading to associated regime shifts in marine ecosystems. These often impact commercial fisheries and societies dependent on them. In a region where in situ hydrographic and biological marine data are scarce, this study uses a combination of remote sensing and ocean modelling to show how a stable seasonal upwelling off the Kenyan coast shifted into the territorial waters of neighboring Tanzania under the influence of the unique 1997/ 98 El Niño and positive Indian Ocean Dipole event. The formation of an anticyclonic gyre adjacent to the Kenyan/ Tanzanian coast led to a reorganization of the surface currents and caused the southward migration of the Somali–Zanzibar confluence zone and is attributed to anomalous wind stress curl over the central Indian Ocean. This caused the lowest observed chlorophyll-a over the North Kenya banks (Kenya), while it reached its historical maximum off Dar Es Salaam (Tanzanian waters). We demonstrate that this situation is specific to the 1997/ 98 El Niño when compared with other the super El-Niño events of 1972,73, 1982–83 and 2015–16. Despite the lack of available fishery data in the region, the local ecosystem changes that the shift of this upwelling may have caused are discussed based on the literature. The likely negative impacts on local fish stocks in Kenya, affecting fishers’ livelihoods and food security, and the temporary increase in pelagic fishery species’ productivity in Tanzania are highlighted. Finally, we discuss how satellite observations may assist fisheries management bodies to anticipate low productivity periods, and mitigate their potentially negative economic impacts.</p>

Geomorphology of Aldabra Atoll

1971 ◽  
Vol 260 (836) ◽  
pp. 31-66 ◽  
Keyword(s):  
Indian Ocean ◽  
Coral Reefs ◽  
Sea Level ◽  
Bottom Topography ◽  
East African ◽  
Southwest Indian Ocean ◽  
Sea Floor ◽  
Regional Setting ◽  
The North ◽  
Central Indian Ocean

1. Regional setting Aldabra Atoll (latitude 9° 24' S, longitude 46° 20' E) is situated 420 km northwest of Madagascar and 640 km from the East African mainland, in the southwest Indian Ocean (figure 1). It forms one of a group of slightly elevated coral reefs to the north of Madagascar, and is thus distinguished from the sea-level coral reefs of the Farquhar group, the Amirantes, and the central Indian Ocean. The raised reefs of Aldabra, Assumption, Cosmoledo and Astove are situated on the summits of mountains approximately 4000 m high, rising from a fairly flat sea floor between 4000 and 4300 m deep. Aldabra and Assumption cap two neighbouring peaks, which are distinct at depths shallower than 2500 m, and Cosmoledo and Astove another pair, distinct above the 2000 m level (figure 2). The general bottom topography round these islands is based on surveys by H.M.S. Owen in 1962. More detailed surveys have been made of Aldabra itself, by H.M.S. Owen in 1962 and H.M.S. Vidal in 1967, and these soundings are contoured in figure 3.

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