Seasonal variations in the Indian Ocean along 110°E. IV. Primary production

1969 ◽  
Vol 20 (1) ◽  
pp. 65 ◽  
Author(s):  
HR Jitts
Keyword(s):  
Indian Ocean ◽  
Primary Production ◽  
Seasonal Variations ◽  
High Productivity ◽  
Photosynthetic Organisms ◽  
South Indian ◽  
Daily Rate ◽  
Deep Layers ◽  
Equatorial Upwelling ◽  
The Indian Ocean

Mean productivity (light saturated photosynthesis), Ps, for the meridian rose from 50 mg C/(hr m²) in August 1962 to a maximum of 62 in October, then fell to a minimum of 4 in January, whereafter it rose slowly to 25 in April-May, then sharply to 45 in late May, and remained at that level till August 1963. Mean Ps for the year was 37 mg C/(hr m²). The depth of the layer of photosynthetic organisms varied between 130 m in October and 60 m in January, with a mean of 85 m. Maximum Ps occurred at 25 m in 36% of the stations, at 0 m in 29 %, and at 50 m in 24%. In January-February the whole meridian was occupied by waters of low productivity, approximately 4 mg C/(hr m²) from the centre of the south Indian Ocean. In April-May the Ps remained uniform along the meridian but rose to 24. At other times four latitudinal intervals along the meridian, with distinctive seasonal variations of productivity characteristics, were found. From 9 to 15°S., waters with high Ps (69 mg C/(hr m²)), and sharp stratification at 50 m, caused by equatorial upwelling, occurred from May to October. From 15 to 24 and 24 to 30°S., waters with high Ps (60 mg Cl(hr m²) and (100 m) deep layers of photosynthetic organisms were found during October-November and May-July respectively. From 30 to 32�S., waters of high productivity (70 mg C/(hr m²)) and a deep layer (100 m) were found in the period July-August. The daily rate of primary production, Pa, of the whole meridian varied from 0.13 g C/(day m²) in August to 0.08 from October to early May, rising sharply in late May to 0.18 and again in early August to 0.27. The depth of the euphotic layer varied between 76 m in October and 63 m in July-August, with a mean of 68 m.

Intraseasonal-to-Interannual Variability of South Indian Ocean Sea Level and Thermocline: Remote versus Local Forcing

2012 ◽  
Vol 42 (4) ◽  
pp. 602-627 ◽  
Author(s):  
Laurie L. Trenary ◽  
Weiqing Han
Keyword(s):  
Indian Ocean ◽  
Interannual Variability ◽  
Sea Level ◽  
Time Scales ◽  
Ekman Pumping ◽  
Remote Forcing ◽  
South Indian ◽  
The Pacific ◽  
The Indian Ocean ◽  
Thermocline Variability

Abstract The relative importance of local versus remote forcing on intraseasonal-to-interannual sea level and thermocline variability of the tropical south Indian Ocean (SIO) is systematically examined by performing a suite of controlled experiments using an ocean general circulation model and a linear ocean model. Particular emphasis is placed on the thermocline ridge of the Indian Ocean (TRIO; 5°–12°S, 50°–80°E). On interannual and seasonal time scales, sea level and thermocline variability within the TRIO region is primarily forced by winds over the Indian Ocean. Interannual variability is largely caused by westward propagating Rossby waves forced by Ekman pumping velocities east of the region. Seasonally, thermocline variability over the TRIO region is induced by a combination of local Ekman pumping and Rossby waves generated by winds from the east. Adjustment of the tropical SIO at both time scales generally follows linear theory and is captured by the first two baroclinic modes. Remote forcing from the Pacific via the oceanic bridge has significant influence on seasonal and interannual thermocline variability in the east basin of the SIO and weak impact on the TRIO region. On intraseasonal time scales, strong sea level and thermocline variability is found in the southeast tropical Indian Ocean, and it primarily arises from oceanic instabilities. In the TRIO region, intraseasonal sea level is relatively weak and results from Indian Ocean wind forcing. Forcing over the Pacific is the major cause for interannual variability of the Indonesian Throughflow (ITF) transport, whereas forcing over the Indian Ocean plays a larger role in determining seasonal and intraseasonal ITF variability.

Interannual Variability in Sea Surface Height at Southern Midlatitudes of the Indian Ocean

2021 ◽  
Vol 51 (5) ◽  
pp. 1595-1609
Author(s):  
Motoki Nagura ◽  
Michael J. McPhaden
Keyword(s):  
Indian Ocean ◽  
Interannual Variability ◽  
Sea Surface Height ◽  
Wind Forcing ◽  
Sea Surface ◽  
The South ◽  
South Indian Ocean ◽  
Eastern Boundary ◽  
South Indian ◽  
The Indian Ocean

AbstractThis study examines interannual variability in sea surface height (SSH) at southern midlatitudes of the Indian Ocean (10°–35°S). Our focus is on the relative role of local wind forcing and remote forcing from the equatorial Pacific Ocean. We use satellite altimetry measurements, an atmospheric reanalysis, and a one-dimensional wave model tuned to simulate observed SSH anomalies. The model solution is decomposed into the part driven by local winds and that driven by SSH variability radiated from the western coast of Australia. Results show that variability radiated from the Australian coast is larger in amplitude than variability driven by local winds in the central and eastern parts of the south Indian Ocean at midlatitudes (between 19° and 33°S), whereas the influence from eastern boundary forcing is confined to the eastern basin at lower latitudes (10° and 17°S). The relative importance of eastern boundary forcing at midlatitudes is due to the weakness of wind stress curl anomalies in the interior of the south Indian Ocean. Our analysis further suggests that SSH variability along the west coast of Australia originates from remote wind forcing in the tropical Pacific, as is pointed out by previous studies. The zonal gradient of SSH between the western and eastern parts of the south Indian Ocean is also mostly controlled by variability radiated from the Australian coast, indicating that interannual variability in meridional geostrophic transport is driven principally by Pacific winds.

scholarly journals The ballast effect of lithogenic matter and its influences on the carbon fluxes in the Indian Ocean

2019 ◽  
Vol 16 (2) ◽  
pp. 485-503 ◽  
Author(s):  
Tim Rixen ◽  
Birgit Gaye ◽  
Kay-Christian Emeis ◽  
Venkitasubramani Ramaswamy
Keyword(s):  
Indian Ocean ◽  
Organic Carbon ◽  
Spatial Variability ◽  
Primary Production ◽  
Carbon Flux ◽  
Carbon Fluxes ◽  
Matter Content ◽  
Organic Carbon Flux ◽  
The Indian Ocean ◽  
Organic Carbon Fluxes

Abstract. Data obtained from long-term sediment trap experiments in the Indian Ocean in conjunction with satellite observations illustrate the influence of primary production and the ballast effect on organic carbon flux into the deep sea. They suggest that primary production is the main control on the spatial variability of organic carbon fluxes at most of our study sites in the Indian Ocean, except at sites influenced by river discharges. At these sites the spatial variability of organic carbon flux is influenced by lithogenic matter content. To quantify the impact of lithogenic matter on the organic carbon flux, the densities of the main ballast minerals, their flux rates and seawater properties were used to calculate sinking speeds of material intercepted by sediment traps. Sinking speeds in combination with satellite-derived export production rates allowed us to compute organic carbon fluxes. Flux calculations imply that lithogenic matter ballast increases organic carbon fluxes at all sampling sites in the Indian Ocean by enhancing sinking speeds and reducing the time of organic matter respiration in the water column. We calculated that lithogenic matter content in aggregates and pellets enhances organic carbon flux rates on average by 45 % and by up to 62 % at trap locations in the river-influenced regions of the Indian Ocean. Such a strong lithogenic matter ballast effect explains the fact that organic carbon fluxes are higher in the low-productive southern Java Sea compared to the high-productive western Arabian Sea. It also implies that land use changes and the associated enhanced transport of lithogenic matter from land into the ocean may significantly affect the CO2 uptake of the organic carbon pump in the receiving ocean areas.

Seasonal variations in the Indian Ocean along 110°E. III. Chlorophylls a and c

1969 ◽  
Vol 20 (1) ◽  
pp. 55 ◽  
Author(s):  
GF Humphrey ◽  
JD Kerr
Keyword(s):  
Regression Analysis ◽  
Indian Ocean ◽  
Water Column ◽  
Chlorophyll A ◽  
Seasonal Variations ◽  
The Indian Ocean ◽  
The Mean

The mean concentrations for all samples analysed were 0.17 �g/l for chlorophyll a and 0.22 �g/I. for chlorophyll c; there were 27 mg/m² of a and 35 mg/m² of c in the water column to 150 m. June-August gave the highest values. The model depth at which concentrations were greatest was 75 m. Diagrams of regression surfaces fitted to the results are given. Regression analysis showed that depth, latitude, and season affected the concentration of chlorophylls; latitude and season affected the column amount of chlorophylls.

Seasonal variations in the Indian Ocean along 110°E. II. Particulate carbon

1969 ◽  
Vol 20 (1) ◽  
pp. 51 ◽  
Author(s):  
BS Newell
Keyword(s):  
Indian Ocean ◽  
Seasonal Variations ◽  
Combustion Method ◽  
Particulate Material ◽  
Particulate Carbon ◽  
The Indian Ocean

Particulate carbon at 0, 50, 100, 150, and 200 m was measured by a combustion method. Mineral carbon appeared to be negligible. Some particulate material escaped the Whatman GF/C filters used. The amount of suspended carbon decreased with depth at most stations from values of 20 �g/l, or more at 0 and 50 m, to 15 �g/l, at 150 m, and 10�g/l, at 150 and 200m. Higher values were found at all depths at the two southernmost stations (25-30 �g/I. at 0 and 50 m decreasing to 15 �gll. at 150 and 200 m ) and at shallow depths at the northernmost stations (20-25 �g/l. at 0 and 50m). At all stations and at all depths, least carbon occurred in March.

scholarly journals Dynamics of the seasonal variations in the Indian Ocean from TOPEX/POSEIDON sea surface height and an ocean model

1998 ◽  
Vol 25 (11) ◽  
pp. 1915-1918 ◽  
Author(s):  
Jiayan Yang ◽  
Lisan Yu ◽  
Chester J. Koblinsky ◽  
David Adamec
Keyword(s):  
Indian Ocean ◽  
Seasonal Variations ◽  
Sea Surface Height ◽  
Ocean Model ◽  
Sea Surface ◽  
The Indian Ocean

Impact of desert and volcanic aerosol deposition on phytoplankton in the South Indian Ocean and Southern Ocean

2020 ◽  
Author(s):  
Carla Geisen ◽  
Celine Ridame ◽  
Emilie Journet ◽  
Benoit Caron ◽  
Dominique Marie ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Southern Ocean ◽  
Primary Production ◽  
Algal Growth ◽  
Biological Response ◽  
South Indian Ocean ◽  
Desert Dust ◽  
South Indian ◽  
Natural Aerosols ◽  
Fe Addition

<p>The Southern Ocean is known to be the largest High Nutrient Low Chlorophyll (HNLC) area of the global ocean, where algal development is mainly limited by iron (Fe) deficiency, except in few naturally Fefertilized areas (e.g. around Kerguelen plateau). The availability of different nutrients is unevenly distributed in this area. Thus, northwards the polar front, nitrogen and phosphorus (N and P) concentrations are high, but the scarcity of silicon (Si) limits the growth of diatoms (HN-LSi-LC). Further North, the Southern Indian Ocean is characterized by macronutrient limitation and low primary production (LNLC).</p><p>In these areas, atmospheric input could play a major role in the nutrient supply of primary producers. The main aim of this study is to assess the biological response of local phytoplankton communities to a deposition of two types of natural aerosols: desert dust and volcanic ash. Preliminary trace-metal clean laboratory experiments enabled us to quantify the abiotic dissolution of main macro- and micronutrients in dry and wet deposition mode of different natural aerosols of these types that yield us to choose Patagonia dust and ash from the Icelandic volcano Eyjafjallajökull for our experiment at sea.</p><p><br>We set up a series of on-board trace-metal clean microcosm experiments in the contrasted biogeochemical conditions of the South Indian Ocean and Southern Ocean with addition of realistic amounts of dust and ash of respectively 2 and 25 mg.L<sup>-1</sup>. Experiments ran over 48 hours to evaluate the triggered primary production and cell abundances. Primary production was estimated by <sup>13</sup>C spike and biogenic Si (bSi) uptake rates were assessed by <sup>30</sup>Si spike. Parallel experiments with nutrient addition (dFe, DIP, DIN and dSi) along with flux cytometry for estimation of pico- and nanophytoplankton cells enabled us to determine which element(s) dissolved from the aerosols was responsible for the enhanced algal growth.</p><p><br>The highest CO<sub>2</sub> fixation rate of 50 mg.m<sup>-3</sup>.day<sup>-1</sup> was found at the natural Fe fertilized Kerguelen plateau station. Dust, ash and Fe addition triggered primary production, and CO<sub>2</sub> fixation doubled in these treatments. We recorded an enrichment of b<sup>30</sup>Si, indicating an increase of Si uptake rate, mostly stimulated by Fe addition. At the different HNLC stations (high N - low Si and high N - high Si), Fe and aerosol addition induced as well increased CO<sub>2</sub> fixation. In the northern LNLC stations, algal growth was stimulated by nitrogen addition as expected, but Fe, Si and aerosol addition also triggered a biological response from <em>Synechococcus</em> cyanobacteria and pico- and nanoeukaryotes.</p><p><br>Noteworthy, in most experiments the two contrasted aerosol types (desert dust and volcanic ash) at particle charges which varied over more than an order of magnitude triggered very similar biological responses in all of the sampled areas, even with distinct elementary and mineral compositions (e.g. the Icelandic volcano ash is 64 % amorphous and contains roughly twice the amount of Fe, P, Mn and<br>Zn compared to the Patagonian desert dust which is only 48 % amorphous).</p>

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