Madhupratap,M.,Gopalakrishnan,T.C.,Haridas,P.,Nair,K.K.C.
Mesozooplankton biomass, composition and distribution in the Arabian Sea during the Fall Intermonsoon: implications of oxygen gradients Journal Article
In: Deep-Sea Research Part II, vol. 48, no. 146, pp. 1345-1368, 2001.
Abstract | BibTeX | Tags: Arabian Sea, depth, diel, Distribution, migration, oxygen minimum, seasonal variation, south, thermocline
@article{,
title = {Mesozooplankton biomass, composition and distribution in the Arabian Sea during the Fall Intermonsoon: implications of oxygen gradients},
author = {Madhupratap,M.,Gopalakrishnan,T.C.,Haridas,P.,Nair,K.K.C.},
year = {2001},
date = {2001-01-01},
journal = {Deep-Sea Research Part II},
volume = {48},
number = {146},
pages = {1345-1368},
abstract = {Mesozooplankton biomass and distribution of calanoid copepods were studied for the upper 500m between 3 and 21§N along an open-ocean transect in the Arabian Sea during the Fall Intermonsoon (September-October 1992, 1993). The region studied has strong gradients in the oxygen minimum zone (OMZ), being acutely deficient in oxygen in the north and with increasing concentrations towards the south. In the upper layers, mesozooplankton biomass was higher in the northern latitudes, above the thermocline, apparently avoiding the OMZ. In the deeper strata, relatively higher biomass was observed in the more oxygenated southern latitudes. Highest mesozooplankton biomass in open waters of the Arabian Sea was observed during the intermonsoon seasons. Calanoid copepods occurred at all depths, and surface-living species did not undertake conspicuous diel migrations, even when they occurred in the deeper waters of the more southern latitudes. A few species belonging to the families Metridinidae and Augaptilidae appeared to be characteristic of the poorly oxygenated mid-depths of the more northern latitudes. Seasonal variations in the composition of the copepod community were negligible. The evolution of the OMZ in the Arabian Sea and its implications are discussed.},
keywords = {Arabian Sea, depth, diel, Distribution, migration, oxygen minimum, seasonal variation, south, thermocline},
pubstate = {published},
tppubtype = {article}
}
Mesozooplankton biomass and distribution of calanoid copepods were studied for the upper 500m between 3 and 21§N along an open-ocean transect in the Arabian Sea during the Fall Intermonsoon (September-October 1992, 1993). The region studied has strong gradients in the oxygen minimum zone (OMZ), being acutely deficient in oxygen in the north and with increasing concentrations towards the south. In the upper layers, mesozooplankton biomass was higher in the northern latitudes, above the thermocline, apparently avoiding the OMZ. In the deeper strata, relatively higher biomass was observed in the more oxygenated southern latitudes. Highest mesozooplankton biomass in open waters of the Arabian Sea was observed during the intermonsoon seasons. Calanoid copepods occurred at all depths, and surface-living species did not undertake conspicuous diel migrations, even when they occurred in the deeper waters of the more southern latitudes. A few species belonging to the families Metridinidae and Augaptilidae appeared to be characteristic of the poorly oxygenated mid-depths of the more northern latitudes. Seasonal variations in the composition of the copepod community were negligible. The evolution of the OMZ in the Arabian Sea and its implications are discussed.
Hitchcock,G.L.,Key,E.L.,Masters,J.
The fate of upwelled waters in the Great Whirl, August 1995 Journal Article
In: Deep-Sea Research Part II, vol. 47, no. 111, pp. 1605-1621, 2000.
Abstract | BibTeX | Tags: Arabian Sea, chlorophyll, Distribution, temperature, thermocline, Upwelling
@article{,
title = {The fate of upwelled waters in the Great Whirl, August 1995},
author = {Hitchcock,G.L.,Key,E.L.,Masters,J.},
year = {2000},
date = {2000-01-01},
journal = {Deep-Sea Research Part II},
volume = {47},
number = {111},
pages = {1605-1621},
abstract = {The Great Whirl is a large, anticyclonic gyre that develops of the northern Somali coast during the Southwest Monsoon. In August 1995 the NOAA Ship Malcolm Baldrige surveyed the seaward edge of the upwelling zone associated with this gyre. The fate of recently upwelled water was followed by mapping surface property distributions along a cool surface feature that extended seaward along the northern edge of the Great Whirl. Surface properties (T, S, and chlorophyll a), surface velocity (ADCP), and XBT and CTD casts were interpreted in relation to the trajectories of three instrumented surface drifters deployed in the feature. Cool surface waters correspond in space to the shoaling of the upper thermocline and offshore advection from the coast. Surface chlorophyll a concentrations decreased from 2 to 3 æg l-1 in the Upwelling zone to 0.5-1.5 æg l-1 in the surface feature and contiguous waters. Maximum surface velocities in the Great Whirl were 250 cm s-1 with velocities >100 cm s-1 along the northern perimeter of the gyre. Decorrelation time-scales for u and v velocity components, and chlorophyll a fluorescence, from the drifters were on the order of 4 to 7 days. These times are comparable to those over which the drifters were ejected from the Great Whirl into the Socotra Gyre. Decorrelation times for sea-surface temperature were somewhat longer (10 days). All three platforms passed between the Somali coast and Socotra within a week of their deployment and then traveled east into the northern Arabian Sea.},
keywords = {Arabian Sea, chlorophyll, Distribution, temperature, thermocline, Upwelling},
pubstate = {published},
tppubtype = {article}
}
The Great Whirl is a large, anticyclonic gyre that develops of the northern Somali coast during the Southwest Monsoon. In August 1995 the NOAA Ship Malcolm Baldrige surveyed the seaward edge of the upwelling zone associated with this gyre. The fate of recently upwelled water was followed by mapping surface property distributions along a cool surface feature that extended seaward along the northern edge of the Great Whirl. Surface properties (T, S, and chlorophyll a), surface velocity (ADCP), and XBT and CTD casts were interpreted in relation to the trajectories of three instrumented surface drifters deployed in the feature. Cool surface waters correspond in space to the shoaling of the upper thermocline and offshore advection from the coast. Surface chlorophyll a concentrations decreased from 2 to 3 æg l-1 in the Upwelling zone to 0.5-1.5 æg l-1 in the surface feature and contiguous waters. Maximum surface velocities in the Great Whirl were 250 cm s-1 with velocities >100 cm s-1 along the northern perimeter of the gyre. Decorrelation time-scales for u and v velocity components, and chlorophyll a fluorescence, from the drifters were on the order of 4 to 7 days. These times are comparable to those over which the drifters were ejected from the Great Whirl into the Socotra Gyre. Decorrelation times for sea-surface temperature were somewhat longer (10 days). All three platforms passed between the Somali coast and Socotra within a week of their deployment and then traveled east into the northern Arabian Sea.
Kinkade,C.S.,Marra,J.,Dickey,T.D.,Langdon,C.,Sigurdson,D.E.,Weller,R.
Diel bio-optical variability observed from moored sensors in the Arabian Sea Journal Article
In: Deep-Sea Research Part II, vol. 46, no. 136, pp. 1813-1831, 1999.
Abstract | BibTeX | Tags: Arabian Sea, diel, growth, thermocline
@article{,
title = {Diel bio-optical variability observed from moored sensors in the Arabian Sea},
author = {Kinkade,C.S.,Marra,J.,Dickey,T.D.,Langdon,C.,Sigurdson,D.E.,Weller,R.},
year = {1999},
date = {1999-01-01},
journal = {Deep-Sea Research Part II},
volume = {46},
number = {136},
pages = {1813-1831},
abstract = {As part of the Forced Upper Ocean Dynamics Program, which ran concurrently with the US JGOFS Arabian Sea Expedition, five moorings were deployed in the historical axis of the Findlater Jet. In addition to other variables, moored sensors collected photosynthetically active radiation (PAR), particulate beam attenuation (Cp), stimulated fluorescence (FLU), and dissolved oxygen (O2) data from October 1994 to October 1995. Diel bio-optical signals were recorded during two periods between the Northeast and Southwest Monsoons at 10, 35, and 65 m. Spectral analysis shows significant diel cycles of Cp, FLU, and O2, but the strength of these cycles was not constant over time. Daily periodicity was lowest for all bio-optical signals just after a strong storm during the 1994 Fall Intermonsoon period. During a phytoplankton bloom associated with a cool advective feature, the FLU and O2 diel signals were most pronounced. Although these signals are biological responses to the daily cycle of irradiance, they are mediated by hydrographic conditions; strongest when phytoplankton are confined within the mixed layer or thermocline, and thus exposed to light intensities long enough to display these responses to PAR. Fluorescence quenching at 10 m due to high irradiance (~1000 æEinstein m-2 s-1) forced the ratio of fluorescence to particulate attenuation into a diel periodicity at 10 m, but not at 35 m (noontime irradiance ~200 æEinstein m-2 s-1), where the FLU and Cp increases were almost in phase. Diel changes in Cp, when scaled to particulate organic carbon, suggest a net production of ~20 mg C m-3 d-1 at 10 and 35 m. We estimate a specific growth rate from a calculated particle production rate balanced by a constant grazing over 24 h to be 0.77 d-1, and using a C*c of 424 mg C m-2, estimate a carbon : chl a ratio between 85 and 115 for a 10-d window during the 1994 Fall Intermonsoon period },
keywords = {Arabian Sea, diel, growth, thermocline},
pubstate = {published},
tppubtype = {article}
}
As part of the Forced Upper Ocean Dynamics Program, which ran concurrently with the US JGOFS Arabian Sea Expedition, five moorings were deployed in the historical axis of the Findlater Jet. In addition to other variables, moored sensors collected photosynthetically active radiation (PAR), particulate beam attenuation (Cp), stimulated fluorescence (FLU), and dissolved oxygen (O2) data from October 1994 to October 1995. Diel bio-optical signals were recorded during two periods between the Northeast and Southwest Monsoons at 10, 35, and 65 m. Spectral analysis shows significant diel cycles of Cp, FLU, and O2, but the strength of these cycles was not constant over time. Daily periodicity was lowest for all bio-optical signals just after a strong storm during the 1994 Fall Intermonsoon period. During a phytoplankton bloom associated with a cool advective feature, the FLU and O2 diel signals were most pronounced. Although these signals are biological responses to the daily cycle of irradiance, they are mediated by hydrographic conditions; strongest when phytoplankton are confined within the mixed layer or thermocline, and thus exposed to light intensities long enough to display these responses to PAR. Fluorescence quenching at 10 m due to high irradiance (~1000 æEinstein m-2 s-1) forced the ratio of fluorescence to particulate attenuation into a diel periodicity at 10 m, but not at 35 m (noontime irradiance ~200 æEinstein m-2 s-1), where the FLU and Cp increases were almost in phase. Diel changes in Cp, when scaled to particulate organic carbon, suggest a net production of ~20 mg C m-3 d-1 at 10 and 35 m. We estimate a specific growth rate from a calculated particle production rate balanced by a constant grazing over 24 h to be 0.77 d-1, and using a C*c of 424 mg C m-2, estimate a carbon : chl a ratio between 85 and 115 for a 10-d window during the 1994 Fall Intermonsoon period
Morrison,J.M.,Codispoti,L.A.,Smith,S.L.,Wishner,K.,Flagg,C.,Gardner,W.D.,Gaurin,S.,Naqvi,S.W.A.,Manghnani,V.,Prosperie,L.,Gundersen,J.S.
The oxygen minimum zone in the Arabian Sea during 1995 Journal Article
In: Deep-Sea Research Part II, vol. 46, no. 174, pp. 1903-1931, 1999.
Abstract | BibTeX | Tags: acoustic, Arabian Sea, density, depth, diel, Distribution, location, migrate, migration, occurrence, oxygen minimum, plankton, thermocline, zooplankton
@article{,
title = {The oxygen minimum zone in the Arabian Sea during 1995},
author = {Morrison,J.M.,Codispoti,L.A.,Smith,S.L.,Wishner,K.,Flagg,C.,Gardner,W.D.,Gaurin,S.,Naqvi,S.W.A.,Manghnani,V.,Prosperie,L.,Gundersen,J.S.},
year = {1999},
date = {1999-01-01},
journal = {Deep-Sea Research Part II},
volume = {46},
number = {174},
pages = {1903-1931},
abstract = {This paper focuses on the characteristics of the oxygen minimum zone (OMZ) as observed in the Arabian Sea over the complete monsoon cycle of 1995. Dissolved oxygen, nitrite, nitrate and density values are used to delineate the OMZ, as well as identify regions where denitrification is observed. The suboxic conditions within the northern Arabian Sea are documented, as well as biological and chemical consequences of this phenomenon. Overall, the conditions found in the suboxic portion of the water column in the Arabian Sea were not greatly different from what has been reported in the literature with respect to oxygen, nitrate and nitrite distributions. Within the main thermocline, portions of the OMZ were found that were suboxic (oxygen less than ~4.5 æM) and contained secondary nitrite maxima with concentrations that sometimes exceeded 6.0 æM, suggesting active nitrate reduction and denitrification. Although there may have been a reduction in the degree of suboxia during the Southwest monsoon, a dramatic seasonality was not observed, as has been suggested by some previous work. In particular, there was not much evidence for the occurrence of secondary nitrite maxima in waters with oxygen concentrations greater than 4.5 æM. Waters in the northern Arabian Sea appear to accumulate larger nitrate deficits due to longer residence times even though the denitrification rate might be lower, as evident in the reduced nitrite concentrations in the northern part of the basin. Organism distributions showed string relationships to the oxygen profiles, especially in locations where the OMZ was pronounced, but the biological responses to the OMZ varied with type of organism. The regional extent of intermediate nepheloid layers in our data corresponds well with the region of the secondary nitrite maximum. This is a region of denitrification, and the presence and activities of bacteria are assumed to cause the increase in particles. ADCP acoustic backscatter measurements show diel vertical migration of plankton or nekton and movement into the OMZ. Daytime acoustic returns from depth were strong, and the dawn sinking and dusk rise of the fauna were obvious. However, at night the biomass remaining in the suboxic zone was so low that no ADCP signal was detectable at these depths. There are at least two groups of organisms, one that stays in the upper mixed layer and another that makes daily excursions. A subsurface zooplankton peak in the lower OMZ (near the lower 4.5 æM oxycline) was also typically present; these animals occurred day and night and did not vertically migrate.},
keywords = {acoustic, Arabian Sea, density, depth, diel, Distribution, location, migrate, migration, occurrence, oxygen minimum, plankton, thermocline, zooplankton},
pubstate = {published},
tppubtype = {article}
}
This paper focuses on the characteristics of the oxygen minimum zone (OMZ) as observed in the Arabian Sea over the complete monsoon cycle of 1995. Dissolved oxygen, nitrite, nitrate and density values are used to delineate the OMZ, as well as identify regions where denitrification is observed. The suboxic conditions within the northern Arabian Sea are documented, as well as biological and chemical consequences of this phenomenon. Overall, the conditions found in the suboxic portion of the water column in the Arabian Sea were not greatly different from what has been reported in the literature with respect to oxygen, nitrate and nitrite distributions. Within the main thermocline, portions of the OMZ were found that were suboxic (oxygen less than ~4.5 æM) and contained secondary nitrite maxima with concentrations that sometimes exceeded 6.0 æM, suggesting active nitrate reduction and denitrification. Although there may have been a reduction in the degree of suboxia during the Southwest monsoon, a dramatic seasonality was not observed, as has been suggested by some previous work. In particular, there was not much evidence for the occurrence of secondary nitrite maxima in waters with oxygen concentrations greater than 4.5 æM. Waters in the northern Arabian Sea appear to accumulate larger nitrate deficits due to longer residence times even though the denitrification rate might be lower, as evident in the reduced nitrite concentrations in the northern part of the basin. Organism distributions showed string relationships to the oxygen profiles, especially in locations where the OMZ was pronounced, but the biological responses to the OMZ varied with type of organism. The regional extent of intermediate nepheloid layers in our data corresponds well with the region of the secondary nitrite maximum. This is a region of denitrification, and the presence and activities of bacteria are assumed to cause the increase in particles. ADCP acoustic backscatter measurements show diel vertical migration of plankton or nekton and movement into the OMZ. Daytime acoustic returns from depth were strong, and the dawn sinking and dusk rise of the fauna were obvious. However, at night the biomass remaining in the suboxic zone was so low that no ADCP signal was detectable at these depths. There are at least two groups of organisms, one that stays in the upper mixed layer and another that makes daily excursions. A subsurface zooplankton peak in the lower OMZ (near the lower 4.5 æM oxycline) was also typically present; these animals occurred day and night and did not vertically migrate.
Brock,J.C.,McClain,C.R.,Hay,W.W.
A southwest monsoon hydrographic climatology for the northwestern Arabian Sea Journal Article
In: Journal of Geophysical Research, vol. 97, no. 337, pp. 9455-9465, 1992.
Abstract | BibTeX | Tags: Antarctic, Arabian Sea, depth, oceanography, Oman, salinity, temperature, thermocline, Upwelling
@article{,
title = {A southwest monsoon hydrographic climatology for the northwestern Arabian Sea},
author = {Brock,J.C.,McClain,C.R.,Hay,W.W.},
year = {1992},
date = {1992-01-01},
journal = {Journal of Geophysical Research},
volume = {97},
number = {337},
pages = {9455-9465},
abstract = {This paper provides a detailed hydrographic climatology for the shallow northwestern Arabian Sea prior to and during the southwest monsoon, presented as multiple-year composite vertical hydrographic sections based on National Oceanographic Data Center historical ocean station data, Temperature and salinity measurements are used to infer the water masses present in the upper 500 m. The hydrographic evolution depicted on bimonthly sections is inferred to result from wind-driven physical processes. In the northwestern Arabian Sea the water mass in the upper 50 m is the Arabian Sea Surface Water. Waters from 50 to 500 m are formed by mixing of Arabian Sea Surface Water with Antarctic and Indonesian intermediate waters. The inflow of Persian Gulf Water does not significantly influence the hydrography of the northwestern Arabian Sea along the Omani coast. Nitrate has a high inverse correlation with temperature and oxygen in the premonsoon thermocline in the depth interval 5(}-150 m. During the southwest monsoon coastal upwelling off Oman and adjacent offshore upward Ekman pumping alter the shallow hydrography.},
keywords = {Antarctic, Arabian Sea, depth, oceanography, Oman, salinity, temperature, thermocline, Upwelling},
pubstate = {published},
tppubtype = {article}
}
This paper provides a detailed hydrographic climatology for the shallow northwestern Arabian Sea prior to and during the southwest monsoon, presented as multiple-year composite vertical hydrographic sections based on National Oceanographic Data Center historical ocean station data, Temperature and salinity measurements are used to infer the water masses present in the upper 500 m. The hydrographic evolution depicted on bimonthly sections is inferred to result from wind-driven physical processes. In the northwestern Arabian Sea the water mass in the upper 50 m is the Arabian Sea Surface Water. Waters from 50 to 500 m are formed by mixing of Arabian Sea Surface Water with Antarctic and Indonesian intermediate waters. The inflow of Persian Gulf Water does not significantly influence the hydrography of the northwestern Arabian Sea along the Omani coast. Nitrate has a high inverse correlation with temperature and oxygen in the premonsoon thermocline in the depth interval 5(}-150 m. During the southwest monsoon coastal upwelling off Oman and adjacent offshore upward Ekman pumping alter the shallow hydrography.