Ishfaq Mir | Geological Survey of India (original) (raw)

Papers by Ishfaq Mir

Journal of Earth System Science, 2009

Monsoon precipitation plays an important role in the socio-economic and agriculture development i... more Monsoon precipitation plays an important role in the socio-economic and agriculture development in the Asian region. Therefore, it is important to understand the monsoon dynamics and its impact on the benthic biogeochemistry. The Bay of Bengal (BOB) receives large quantity of suspended particulate matter and fresh water discharge from the Himalayas and Indian peninsula by a number of major rivers like Ganges-Brahmaputra, Krishna, Godavari, Cauvery and Irrawadi-Salween. The northern BOB receives maximum lithogenic flux during south-west (SW) monsoon that coincides with maximum river discharge from Ganges-Brahmaputra, Krishna- Godavari. In the present study, an attempt has been made to understand the impact of intensified SW monsoonal precipitation on the behaviour of redox-sensitive elements in a sediment core. Reconstruction of paleo-redox conditions in a radiocarbon (14C) dated sediment core (SK-218/1), covering the past 45 ka (thousand calendar years), collected from the western Bay of Bengal (Lat: 14o 02’N; Long: 82o 00’E) at a water depth of 3307 m, has been made based on geochemical analysis of redox-sensitive elements. The high U/Th ratio, Mo enrichment, Mo/U enrichment factor ratio, negative Ce-anomaly and lower Mn/Al and Fe/Al ratio, are all indicative of prevalence of sulfidic conditions in the benthic environment from 15.2 to 4.5 ka, peaking around 9.5 ka. Another event of smaller intensity and duration appears to have occurred around 20.5 ka. At this time, the U enrichment factor (3.1) was close to the Fe (II) – Fe (III) redox boundary and Mo/U enrichment ratio was nearly half that of the seawater, suggesting the prevalence of suboxic conditions. The major event centering around 9.5 ka corresponds to the previously recorded Southwest Monsoon intensification in response to increase in northern hemisphere summer insulation. However, productivity proxies – organic carbon and nitrogen contents – do not indicate marked increase in productivity at this time. It is proposed that as a result of large increase in lithogenic material supplied from land due to southwest monsoon intensification, which is evident by the very high concentrations of Al, Zr and Hf, the flux of fresh labile organic matter reaching the seafloor was higher, the degradation of which led to anoxia in the benthic environment. There is a strong positive correlation (R2=0.97) between Mo and Zr suggesting a coupling between lithogenic flux supplied by the monsoon and development of reducing condition during intensified monsoon between 4.5ka to 15.2ka. Our results suggest that temporal variability of the ballasting effect of the terrestrially-derived material could play a key role in benthic biogeochemistry and ecology of the Bay of Bengal. On the contrary, there is no correlation between Mo and Zr (R2=0.1) from 15.2ka to 45ka (except at 20.5ka) due to weaker monsoon during that period. Therefore, present data clearly shows that monsoon intensification can develop a reducing condition in the Bay of Bengal sediments.

Quaternary International, 2012

Journal of the Geological Society of India, 2013

Journal of Asian Earth Sciences, 2022

Journal of Earth System Science, Aug 10, 2019

Comparison of late Quaternary productivity variation in two contrasting basins of northern Indian... more Comparison of late Quaternary productivity variation in two contrasting basins of northern Indian Ocean using geochemical proxies (POSTER). Abstract: A 4.1m long sediment core (SK-117/GC-08) raised from a water depth of 2500 m in the Eastern Arabian Sea (EAS) (Lat: 15˚29' N; Long: 72˚51' E) is studied for variation of productivity during the last 100 ka utilizing geochemical proxies. The temporal variation in element concentration and fluxes of CaCO3, organic carbon (Corg) and Barium excess (Baexc) together in general indicate a higher productivity during the cold climate and highest during the Last Glacial Maximum in particular. This cold climate-increased productivity coupling may be attributed to the shoaling of nutricline due to enhanced convective mixing resulting from the intensified winter monsoon during cold periods. A radiocarbon dated sediment core (SK-218/1) covering the past 45 ka is collected from the western Bay of Bengal (Lat: 14° 02′N; Long: 82° 00′E) at a wa...

Paleoceanographers have used several proxies for studying paleo-productivity of the of world ocea... more Paleoceanographers have used several proxies for studying paleo-productivity of the of world ocean
basins, eg., biological measures such as microfossil, sediment organic matter, biomarkers etc.
Geochemical proxies such as organic carbon, barium and calcium carbonate components have been
widely used to reconstruct palaeo export production. However, organic carbon has its own limitation
(preservation problems).
In the present study two sediment cores each from two contrasting basins of northern Indian Ocean,
viz Eastern Arabian Sea (EAS) and Western Bay of Bengal (WBOB), both experiencing similar
forcing by seasonally reversing Indian monsoons are studied for understanding the variation in
productivity during the late Quaternary. The study is important in terms of the role of tropical Indian
Ocean in regulating atmospheric carbon-dioxide on glacial-interglacial time-scale.

Monsoon precipitation plays an important role in the socio-economic and agriculture development i... more Monsoon precipitation plays an important role in the socio-economic and agriculture development in the Asian region. Therefore, it is important to understand the monsoon dynamics and its impact on the benthic biogeochemistry. The Bay of Bengal (BOB) receives large quantity of suspended particulate matter and fresh water discharge from the Himalayas and Indian peninsula by a number of major rivers like Ganges-Brahmaputra, Krishna, Godavari, Cauvery and Irrawadi-Salween. The northern BOB receives maximum lithogenic flux during south-west (SW) monsoon that coincides with maximum river discharge from Ganges-Brahmaputra, Krishna- Godavari. In the present study, an attempt has been made to understand the impact of intensified SW monsoonal precipitation on the behaviour of redox-sensitive elements in a sediment core.
Reconstruction of paleo-redox conditions in a radiocarbon (14C) dated sediment core (SK-218/1), covering the past 45 ka (thousand calendar years), collected from the western Bay of Bengal (Lat: 14o 02’N; Long: 82o 00’E) at a water depth of 3307 m, has been made based on geochemical analysis of redox-sensitive elements. The high U/Th ratio, Mo enrichment, Mo/U enrichment factor ratio, negative Ce-anomaly and lower Mn/Al and Fe/Al ratio, are all indicative of prevalence of sulfidic conditions in the benthic environment from 15.2 to 4.5 ka, peaking around 9.5 ka. Another event of smaller intensity and duration appears to have occurred around 20.5 ka. At this time, the U enrichment factor (3.1) was close to the Fe (II) – Fe (III) redox boundary and Mo/U enrichment ratio was nearly half that of the seawater, suggesting the prevalence of suboxic conditions. The major event centering around 9.5 ka corresponds to the previously recorded Southwest Monsoon intensification in response to increase in northern hemisphere summer insulation. However, productivity proxies – organic
carbon and nitrogen contents – do not indicate marked increase in productivity at this time. It is proposed that as a result of large increase in lithogenic material supplied from land due to southwest monsoon intensification, which is evident by the very high concentrations of Al, Zr and Hf, the flux of fresh labile organic matter reaching the seafloor was higher, the degradation of which led to anoxia in the benthic environment. There is a strong positive correlation (R2=0.97) between Mo and Zr suggesting a coupling between lithogenic flux supplied by the monsoon and development of reducing condition during intensified monsoon between 4.5ka to 15.2ka. Our results suggest that temporal variability of the ballasting effect of the terrestrially-derived material could play a key role in benthic biogeochemistry and ecology of the Bay of Bengal. On the contrary, there is no correlation between Mo and Zr (R2=0.1) from 15.2ka to 45ka (except at 20.5ka) due to weaker monsoon during that period. Therefore, present data clearly shows that monsoon intensification can develop a reducing condition in the Bay of Bengal sediments.

Systematic studies on the suspended particulate matter (SPM) measured on a seasonal cycle in the ... more Systematic studies on the suspended particulate matter (SPM) measured on a seasonal cycle in
the Mandovi Estuary, Goa indicate that the average concentrations of SPM at the regular station
are ∼20mg/l, 5mg/l, 19mg/l and 5mg/l for June–September, October–January, February–April
and May, respectively. SPM exhibits low-to-moderate correlation with rainfall indicating that SPM
is also influenced by other processes. Transect stations reveal that the SPM at sea-end stations
of the estuary are at least two orders of magnitude greater than those at the river-end during
the monsoon. Estuarine turbidity maximum (ETM) of nearly similar magnitude occurs at the
same location in two periods, interrupted by a period with very low SPM concentrations. The
ETM occurring in June–September is associated with low salinities; its formation is attributed to
the interactions between strong southwesterly winds (5.1–5.6ms−1) and wind-induced waves and
tidal currents and, dominant easterly river flow at the mouth of the estuary. The ETM occurring
in February–April is associated with high salinity and is conspicuous. The strong NW and
SW winds (3.2–3.7ms−1) and wind-driven waves and currents seem to have acted effectively at
the mouth of the estuary in developing turbidity maximum. The impact of sea breeze appears
nearly same as that of trade winds and cannot be underestimated in sediment resuspension and
deposition.

A 4.1m long sediment core from the Eastern Arabian Sea (EAS) is studied using multiple geochemica... more A 4.1m long sediment core from the Eastern Arabian Sea (EAS) is studied using multiple geochemical
proxies to understand the variation of productivity and terrigenous matter supply during the past 100 ka. The temporal
variation in element concentration and fluxes of CaCO3, organic carbon (Corg) and Barium excess (Baexc), together, in
general indicate a higher productivity during the cold climate and highest during the Last Glacial Maximum (LGM) in
particular. This cold climate-increased productivity coupling may be attributed to the shoaling of nutricline due to
enhanced convective mixing resulting from the intensified winter monsoon. Increased linear sedimentation rates and
fluxes of Al, Fe, Mg, Ti, Cr, Cu, Zn, and V during the cold period also suggest increased input of terrigenous matter
supporting intensified winter winds. However, the presence of large abundance of structurally unsupported elemental
content (e.g.: Mg-86%, Fe-82% and Al-53%) indicate increased input of terrigenous material which was probably
enhanced due to intense winter monsoon.

Aluminium, titanium and iron are the major lithogeneous contributors to the marine sediment and t... more Aluminium, titanium and iron are the major lithogeneous contributors to the marine sediment and their
abundance varies strikingly with the intensity of monsoonal precipitation. Al and Ti concentrations in
a sediment core (SK-129/GC-05) from southeastern Arabian Sea exhibit a very strong positive correlation
(r¼0.92, n¼140) suggesting their lithogenous association, whereas Ti and Fe does not correlate so strongly
(r ¼ 0.44). This suggests that part of Fe is structurally unsupported, as is evident by the two-fold increased
Fe/Al ratio (0.87 average) compared to upper continental crust (0.44). The presence of structurally
unsupported Fe is confirmed by the sequential leaching of Fe which is associated with different fractions
such as exchangeable (0.98%), carbonate (1.98%), FeeMn oxide (30.8%), organic carbon (4.7%) and biogenic
opal (11.4%) which together constitutes nearly 50% of the bulk Fe content. There is a good correlation
between time series Fe/Al and differential solar insolation, suggesting warmer and humid climatic
conditions resulted in intense weathering of hinterland rocks, associated with increased monsoonal
precipitation, which probably decoupled soluble Fe and transported it to the southeastern Arabian Sea.

Reconstruction of paleo-redox conditions in a radiocarbon (14C) dated sediment core (SK-218/1), c... more Reconstruction of paleo-redox conditions in a radiocarbon (14C) dated sediment core (SK-218/1), covering
the past 45 ka (thousand calendar years), collected from the western Bay of Bengal (Lat: 14° 02′N; Long:
82° 00′E) at a water depth of 3307 m, has been made based on redox-sensitive element geochemistry. The
high U/Th ratio, Mo enrichment, Mo/U enrichment factor ratio, Ce/Ce*b1 and lower Mn/Al and Fe/Al ratios,
compared to upper continental crust are all indicative of prevalence of suboxic condition in the benthic environment
from 15.2 ka to 4.5 ka, peaking around 9.5 ka. The suboxic condition around 9.5 ka corresponds
to the previously recorded southwest (SW) monsoon intensification in response to the increase in northern
hemisphere summer insulation. However, productivity proxies – organic carbon and nitrogen contents – do
not indicate marked increase in productivity at this time. It is proposed that as a result of large increase in
lithogenic material supplied from land due to SW monsoon intensification, which is evident by the very
high concentration of Al, Zr and Hf, the flux of fresh labile organic matter and these might have formed
dense mineral matter — biogenic aggregates which sinks rapidly to the seafloor, and the degradation of labile
organic matter might have led to the development of suboxic condition in the benthic environment. There
exists a strong positive correlation (r=0.98) between Mo and Zr during 15.2 ka to 4.5 ka suggesting a coupling
between suboxic condition and lithogenic flux supply by the intensified SW monsoon. Our results suggest
that temporal variability of the ballasting effect of the terrestrially-derived material could play a key role
in benthic biogeochemistry and ecology of the Bay of Bengal.
We also provide the first record of the nitrogen isotopic composition (δ15N) of sedimentary organic matter in
the western Bay of Bengal, a region where the mesopelagic oxygen minimum zone (OMZ) is just short of
being suboxic (denitrifying) today. The sedimentary δ15N fluctuated considerably in the past, especially during
the Marine Isotope Stage 3. Oscillations in δ15N were apparently in concert with those in organic carbon
and nitrogen contents and could be related to climatic changes (Heinrich and Dansgaard–Oeschger events) in
the North Atlantic. The Dansgaard–Oeschger 12 event appears to have exerted the most intense effect on Bay
of Bengal biogeochemistry when surface productivity, as inferred from the organic carbon and nitrogen contents,
was the highest recorded in the core, and the δ15N reached up to 6.3‰. Considering the probable dilution
by isotopically light terrigenous organic matter, it would appear that OMZ of the Bay of Bengal had
turned denitrifying. However, the absence of suboxic conditions in the sediments at this time suggests a
decoupling of the benthic processes with those in the mesopelagic water column.

Journal of Earth System Science, 2009

Quaternary International, 2012

Journal of the Geological Society of India, 2013

Journal of Asian Earth Sciences, 2022

Journal of Earth System Science, Aug 10, 2019

Monsoon precipitation plays an important role in the socio-economic and agriculture development i... more Monsoon precipitation plays an important role in the socio-economic and agriculture development in the Asian region. Therefore, it is important to understand the monsoon dynamics and its impact on the benthic biogeochemistry. The Bay of Bengal (BOB) receives large quantity of suspended particulate matter and fresh water discharge from the Himalayas and Indian peninsula by a number of major rivers like Ganges-Brahmaputra, Krishna, Godavari, Cauvery and Irrawadi-Salween. The northern BOB receives maximum lithogenic flux during south-west (SW) monsoon that coincides with maximum river discharge from Ganges-Brahmaputra, Krishna- Godavari. In the present study, an attempt has been made to understand the impact of intensified SW monsoonal precipitation on the behaviour of redox-sensitive elements in a sediment core.
Reconstruction of paleo-redox conditions in a radiocarbon (14C) dated sediment core (SK-218/1), covering the past 45 ka (thousand calendar years), collected from the western Bay of Bengal (Lat: 14o 02’N; Long: 82o 00’E) at a water depth of 3307 m, has been made based on geochemical analysis of redox-sensitive elements. The high U/Th ratio, Mo enrichment, Mo/U enrichment factor ratio, negative Ce-anomaly and lower Mn/Al and Fe/Al ratio, are all indicative of prevalence of sulfidic conditions in the benthic environment from 15.2 to 4.5 ka, peaking around 9.5 ka. Another event of smaller intensity and duration appears to have occurred around 20.5 ka. At this time, the U enrichment factor (3.1) was close to the Fe (II) – Fe (III) redox boundary and Mo/U enrichment ratio was nearly half that of the seawater, suggesting the prevalence of suboxic conditions. The major event centering around 9.5 ka corresponds to the previously recorded Southwest Monsoon intensification in response to increase in northern hemisphere summer insulation. However, productivity proxies – organic
carbon and nitrogen contents – do not indicate marked increase in productivity at this time. It is proposed that as a result of large increase in lithogenic material supplied from land due to southwest monsoon intensification, which is evident by the very high concentrations of Al, Zr and Hf, the flux of fresh labile organic matter reaching the seafloor was higher, the degradation of which led to anoxia in the benthic environment. There is a strong positive correlation (R2=0.97) between Mo and Zr suggesting a coupling between lithogenic flux supplied by the monsoon and development of reducing condition during intensified monsoon between 4.5ka to 15.2ka. Our results suggest that temporal variability of the ballasting effect of the terrestrially-derived material could play a key role in benthic biogeochemistry and ecology of the Bay of Bengal. On the contrary, there is no correlation between Mo and Zr (R2=0.1) from 15.2ka to 45ka (except at 20.5ka) due to weaker monsoon during that period. Therefore, present data clearly shows that monsoon intensification can develop a reducing condition in the Bay of Bengal sediments.