GEOSCIENCES

Solar influence on the intensity of the Indian monsoon is demonstrated using a sediment core from the eastern Arabian Sea dating back to 1200 yr, through pattern matching as well as spectral analysis of proxy records of monsoon and solar activity. The intensity of the Indian monsoon is found to have decreased during periods of solar minima during the last millennium. Periodicities of 200 þ 20, 105 þ 15 and 60 þ 10 yr are observed in the proxy records coinciding with those known for solar cycles. The V60-yr periodicity observed in the instrumental rainfall data appears to be of solar origin and supports the hypothesis of solar control on the Indian monsoon on a multi-decadal time scale. Evidence for the presence of a coupled atmospheric forcing for the Indian and East African monsoons on a centennial time scale is also seen.

Water-soluble ionic constituents (Cl-, NO 3-, SO 4 2-, Na + , NH 4 + , K + , Mg 2+ and Ca 2+) of PM 2.5 were measured using Ambient Ion Monitor coupled-to Ion Chromatograph (AIM-IC) with a time resolution of one hour at Ahmedabad (an urban location in semi-arid region of western India) during summer and winter to study the diurnal and seasonal variations. Maximum abundances of most of the species were observed during afternoon hours in summer, whereas minimum concentrations were found during winter at the same local time. During summer, the concentration levels of most of the constituents in a diurnal cycle are largely influenced by ambient relative humidity variation. During winter, the emission strength and boundary layer dynamics impact the diurnal cycle. Secondary inorganic species like NH 4 + , NO 3 and SO 4 2exhibit significant differences in their relative abundances during winter and summer. Four factors have been derived by Positive Matrix Factorization (PMF) analysis on water-soluble ionic constituents. These are secondary, sea-salt, mineral dust sources and the fourth factor is associated with K + , which is likely to be biomass burning emission.

A temporal high-resolution analysis of the Sr-Nd isotopic composition, the Fe, Al and V composition and the magnetic susceptibility (MS) has been carried out in a sediment core from the western Bay of Bengal to trace sedimentary sources. Significant variations of the Sr and Nd isotopic composition and corresponding MS and elemental Fe/Al and V/Al ratios are observed in the sediment core with depth (time) indicating variable contributions from sources. The observed changes in the sediment provenance correlate well with the climatic record of the region, highlighting the important influence of climate over erosion. Relatively lower 87 Sr/ 86 Sr and higher ε Nd corresponding to the Last Glacial Maximum (LGM) suggests proportionally reduced sediment contribution from the Himalaya. Erosion rate over the Himalaya decreased during LGM due to combined influence of reduced intensity of the southwestern monsoon and larger extent of glaciations over the Higher Himalaya, the main source of sediments to the Bay of Bengal.

The concentration and isotope composition of dissolved Nd have been measured in the water column along an 87°E transect (GIO1 section of International GEOTRACES Program) in the Bay of Bengal (BoB) to investigate the effect of water mass mixing and Nd release from particulate matter in determining these properties. The concentration of Nd in surface waters of the BoB shows a North-South decreasing non-linear trend ($46 to $22 pmol/kg) with salinity, whereas its depth profiles typically show a high value in surface waters, a minimum ($15 to $23 pmol/kg) in the shallow subsurface ($50-200 m), followed by a gradual increase with depth. The Nd concentration of BoB waters is generally higher than that in nearby oceanic basins. On the other hand, the e Nd values in the BoB are less radiogenic compared to those reported for other regions of the global oceans (except Baffin Bay, the North Atlantic Subpolar Gyre and the Niger delta margin), and show a greater variation in the upper water column. Surface waters of the southernmost profile ($6°N) show a more radiogenic e Nd value $À8, which decreases to À15 in the northernmost profile ($20°N), close to the values for dissolved and particulate phases of the Ganga-Brahmaputra (G-B) Rivers. This latitudinal trend is most likely a result of variations in mixing proportion between the more radiogenic Indonesian Throughflow surface waters (IW) and unradiogenic BoB low salinity water; the former's signature being more clearly discernible in surface waters of the two southernmost profiles ($6°N and $8.5°N). Attempts to balance the Nd budget in the water column based on an inversion model, suggest that in addition to water masses other source(s) is required, the strength of which is estimated to vary from 1% to 65% of the measured Nd concentration. The calculations also show that the e Nd of this additional source(s) has to be in the range of $À16 ± 2, typical of G-B river sediments. These observations, coupled with the North-South distribution of dissolved Nd and e Nd , indicate that this additional source is release from particulate phases supplied by the G-B river system. The calculations also bring out the presence of "hot-spots" of Nd release (excess Nd) near the sediment-water interface along the northern slope of the bay, indicating supply of Nd from continental margin sediments. This study underscores the significant role of dissolved/particulate Nd from the Ganga-Brahmaputra river system in contributing to the dissolved Nd budget of the global oceans.

Pollen, C/N ratios and δ13COM from a 1.2 m thick palaeolake deposit at Sangla, Kinnaur, Himachal Pradesh provide records of climatic changes during the past 10,000 years. The C/N ratios together with pollen data indicate high lake level between 10,000 and 4,000 yrs BP. Following this, an increase in δ13C (+ 2‰) indicates stressed climatic conditions, whereby δ13COM attained a value of–23‰, being the maximum for the available record. This event is bracketed between 3500 and 1500 yrs BP.

Pollen, C/N ratios and δ13COM from a 1.2 m thick palaeolake deposit at Sangla, Kinnaur, Himachal Pradesh provide records of climatic changes during the past 10,000 years. The C/N ratios together with pollen data indicate high lake level between 10,000 and 4,000 yrs BP. Following this, an increase in δ13C (+ 2‰) indicates stressed climatic conditions, whereby δ13COM attained a value of–23‰, being the maximum for the available record. This event is bracketed between 3500 and 1500 yrs BP. Subsequently, the lake ...

Radiocarbon (14 C) in atmospheric CO 2 over the Northern Indian Ocean was measured between 1993 and 2001, by collecting remote maritime air from ship cruises. The D 14 C of atmospheric CO 2 over this region decreased from 12073% in 1993 to 8572% in 2001, consistent with the global exponential decreasing trend. The D 14 C values measured in spring of 2001 over the Bay of Bengal and the Arabian Sea were 8672% and 8573%, respectively, thus indistinguishable within error limits. Significant inter-annual variations in D 14 C were observed over this region. Input of 14 C-free fossil fuel CO 2 from the South Asian continent significantly influence springtime D 14 C values over the Northern Indian Ocean, through transport by meridional atmospheric circulation. Additional variations are possibly caused by enhanced inputs of 14 C-rich biogenic CO 2 , during El Nin˜o/Southern Oscillation events.

The concentrations of Ra isotopes (t'oRa,223Ra,228Ra and 226Ra) and 222Rn have been determined in brines from Kharaghoda, western India. The Ra isotopes concentrations in these samples are orders of magnitude higher than that reported in potable groundwaters. The 22aRa activities lie between 28 to 277 dpm per kg; about 4olo to 9606 of that expected from its production, calculated using 222Rn as a recoil flux monitor. The low 1224Ra/222Rn] activity ratios are typical of less saline brines. Retardation factors for Ra in these brines, derived from the 222Rn-22aRa-228Ra system and based on a reversible exchange model, are in the range of about 0.3-l 14. These values are 3-4 orders of magnitude lower than that in potable groundwaters. The residence time of Ra in Kharaghoda brines is approximately one day. Our data suggest that in briny aquifers Ra is considerably less'particle-reactive'than in potable groundwaters. The retardation factor for Ra shows a strong negative correlation with salinity. This anticorrelation suggests that salinity would play a crucial role in determining the mobility of Ra and its geochemical homologues through groundwater systems.

Measurement of natural and man-made 14 C and 3 H and man-made 90 Sr, 239,240 Pu and 241 Am at two GEOSECS stations, GX 413 and 416 reoccupied two decades later are reported. Deeper penetration of nutrient and oxygen-poor intermediate waters along with man-made radionuclides, especially at GX 413 (near Bab el Mandab), are noticeable. The one-dimensional advection-diffusion model using pre-nuclear 14 C data supports this observation as the vertical advection velocity at GX 413 is 11.8 m/y compared to the 3.6 m/y in the central north Arabian Sea (GX 416).

Sr and Nd isotopic composition of silicate fractions of sediments have been measured in two well dated gravity cores from the eastern Arabian Sea archiving a depositional history of ∼29 and ∼40 ka. The 87 Sr/ 86 Sr and " Nd in the northern core (SS-3104G; 12.8°N, 71.7°E) ranges from 0.71416 to 0.71840 and −8.8 to −12.8; these variations are limited compared to those in the southeastern core (SS-3101G; 6.0°N, 74.0°E), in which they vary from 0.71412 to 0.72069 and −9.0 to −15.2 respectively. This suggests that the variation in the relative proportions of sediments supplied from different sources to the core SS-3104G are limited compared to core SS-3101G. The 87 Sr/ 86 Sr and " Nd profiles of SS-3101G exhibit two major excursions, ca. 9 ka and 20 ka, coinciding with periods of Holocene Intensified Monsoon Phase (IMP) and the Last Glacial Maximum (LGM) respectively with more radiogenic 87 Sr/ 86 Sr and lower " Nd during these periods. These excursions have been explained in terms of changes in the erosion patterns in the source regions and surface circulation of the Northern Indian Ocean resulting from monsoon intensity variations. The intensification of NorthEast (NE) monsoon and associated strengthening of the East Indian Coastal Current in southwest direction during LGM transported sediments with higher 87 Sr/ 86 Sr and lower " Nd from the western Bay of Bengal to the Arabian Sea. In contrast, enhanced SouthWest (SW) monsoon at ∼9 ka facilitated the transport of sediments from the northern Arabian Sea, particularly Indus derived, to the southeastern Arabian Sea. This study thus highlights the impact of monsoon variability on erosion patterns and ocean surface currents on the dispersal of sediments in determining the Sr and Nd isotopic composition of sediments deposited in the eastern Arabian Sea during the last ∼40 ka.

The sources are dominated by contributions from the Higher Himalaya (HH) with subordinate supply from the Lesser Himalaya (LH). However, on millennial timescale, there are evidences of variations in the provenance of sediments related to climatic changes (

Indian Ocean Deep waters (IDW) show an increase in salinity and ZCO2 between 64øS and 16+4øN by 0.106-0.110%o and 82-104 gM kg-1 respectively with a corresponding decrease in A•4C by 42%0 as revealed by the GEOSECS data (1977-78). The A•4C-ZCO2-Salinity relationships show better correlation in the western sector. High biological productivity induced changes and corrosive deepwaters could account for ECO2 increase in the northern regions. Reoccupation of GEOSECS stations during 1985-95 do not show distinctly discernible short-term temporal changes in A•4C, ECO2 and salinity. [1976] based on GEOSECS Atlantic data observed decreasing trend in A I4c and a similar trend for salinity m the deep water masses of North Atlantic Deep Water (NADW) and Antarctic Bottom Waters (AABW) between 36øN and 60øS. GEOSECS measurements made in the Indian Ocean [Stuiver and Ostlund, 1983] provide a good database for evaluating spatial variations in this region. As a part of the present study to understand circulation and air-sea exchange of CO2 using •4C [Bhushan et al.

Field stratigraphy, sedimentology and luminescence dating of the exposed fluvial and aeolian sequences from the southern desert margin were used to discern the pattern of southwest monsoon variability during the last 130 ka. The sedimentary architecture and textural attributes of the sediments belonging to the period 130-120 ka suggests the existence of a meandering river system consequent to enhanced southwest monsoon conditions. A shift from a meandering to a braided pattern during 120-100 ka indicates a phase of reduced precipitation. Presence of flood plain fines and bedded calcretes during $100-70 ka suggest a period of enhanced monsoon with seasonality. Following this, a phase of weak monsoon activity was observed during 70-60 ka. Regional flood plain aggradation and pedogenesis during the period o60-30 ka indicated enhanced southwest monsoon condition. Onset of fluvio-aeolian sedimentation after 30 ka and initiation of a regionally extent aeolian sedimentation during 20-11 ka indicates overall dry climatic condition. These observations accord well with the total organic carbon (TOC) data and suggest a vegetation /moisture control on the aeolian sedimentation in the region. Termination of a regional fluvial phase around 30 ka and incision of dunes dated to 20-11 ka suggest that the present rivers occupied their course between o30 ka and 411 ka. Drowned valleys in the estuarine zones suggest that the incision began during the low sea stand around 20 ka when the rivers were graded to the exposed shelf. The incision intensified with the re-establishment of monsoon during the early Holocene.

Eight gravity cores from the active eastern continental margins of the Arabian Sea were dated using 210Pbxs, 137Cs and 14C. The short-term (< or = 100 years) sedimentation rates range from 0.06 to 0.66 cm/year where as the long-term (> or = 1000 years) ones using AMS 14C on planktonic foraminifera varied from 0.004 to 0.13 cm/year. For long-term chronology (< or = 50,000 years) AMS dating of well-cleaned planktonic foraminifera is most suited.

The pattern of strain accumulation and its release during earthquakes along the eastern Himalayan syntaxis is unclear due to its structural complexity and lack of primary surface signatures associated with large-to-great earthquakes. This led to a consensus that these earthquakes occurred on blind faults. Toward understanding this issue, palaeoseismic trenching was conducted across a ~3.1 m high fault scarp preserved along the mountain front at Pasighat (95.33°E, 28.07°N). Multi-proxy radiometric dating employed to the stratigraphic units and detrital charcoals obtained from the trench exposures provide chronological constraint on the discovered palaeoearthquake surface rupture clearly suggesting that the 15(th) August, 1950 Tibet-Assam earthquake (Mw ~ 8.6) did break the eastern Himalayan front producing a co-seismic slip of 5.5 ± 0.7 meters. This study corroborates the first instance in using post-bomb radiogenic isotopes to help identify an earthquake rupture.

The 14 C measurements in the Arabian Sea and the Bay of Bengal during the late 1990s offer a way to assess the temporal changes in the inventories of bomb-14 C and its penetration into the ocean, in two decades since GEOSECS expeditions (1977-1978). The mean penetration depth of bomb radiocarbon during GEOSECS (1977-1978) was 270 m, which increased by $40% to 381 m in 1994-1998. The small changes in bomb-14 C inventories, significant increase in the mean penetration depths and lowering of the surface D 14 C values in the northern Indian Ocean indicate the temporal variation of bomb-14 C in two decades is mainly through downward transfer through mixing with deeper waters. The observed bomb-14 C inventory in the northern Indian Ocean agrees with numerical model simulated values, except at the equatorial Indian Ocean. The high bomb-14 C inventory at the equator can be attributed to lateral advection of 14 C-enriched waters from the Pacific Ocean through the Indonesian archipelago. The air-sea CO 2 exchange rates in the northern Indian Ocean calculated from the bomb-14 C inventories range from $7 mol m À2 yr À1 (in the northern Bay of Bengal) to 20 mol m À2 yr À1 (in the equatorial Indian Ocean). Net sea-air flux of CO 2 estimated for the northern Indian Ocean between 0 and 25 N is $104 AE 30 TgC yr À1. The Bay of Bengal is a net sink of atmospheric CO 2 ($À1 AE 0.4 TgC yr À1), while the Arabian Sea is a source of CO 2 ($69 AE 21 TgC yr À1).

We analyzed a sediment core from the equatorial Arabian Sea, chronologically constrained by accurate accelerator mass spectrometry (AMS) radiocarbon dates on selected planktonic foraminiferal species, for paleoproductivity variations corresponding to the variations in the Indian ...

A compilation of paleoceanographic data and a coupled atmosphere-ocean climate model were used to examine global ocean surface temperatures of the Last Interglacial (LIG) period, and to produce the first quantitative estimate of the role that ocean thermal expansion likely played in driving sea level rise above present day during the LIG. Our analysis of the paleoclimatic data suggests a peak LIG global sea surface temperature (SST) warming of 0.7±0.6°C compared to the late Holocene. Our LIG climate model simulation suggests a slight cooling of global average SST relative to preindustrial conditions (ΔSST =-0.4°C), with a reduction in atmospheric water vapor in the Southern Hemisphere driven by a northward shift of the Intertropical Convergence Zone, and substantially reduced seasonality in the Southern Hemisphere. Taken together, the model and paleoceanographic data imply a minimal contribution of ocean thermal expansion to LIG sea level rise above present day. Uncertainty remains, but it seems unlikely that thermosteric sea level rise exceeded 0.4±0.3 m during the LIG. This constraint, along with estimates of the sea level contributions from the Greenland Ice Sheet, glaciers and ice caps, implies that 4.1 to 5.8 m of sea level rise during the Last Interglacial period was derived from the Antarctic Ice Sheet. These results reemphasize the concern that both the Antarctic and Greenland Ice Sheets may be more sensitive to temperature than widely thought.

Growth year 1960. and soaked in 30% H2O2 for 2 days to remove organic matter. We report 14C ages of the samples below. CH-96. Chikasa Gosa Reef Oyster Collected from Chikasa, Saurashtra (21°45'N, 70°30'E) at 1 m asl. CH-97. Chikasa Gosa Reef Oyster Collected from Chikasa at 1 m asl. CH-98. Chikhli Oyster Collected from Chikhli (20°48'N, 70°52'E) at 4 m asl. CH-99. Patan Bridge Oyster Collected from Patan Bridge over the Hiren River (20°55'N, 70°30'E) at 12 m asl. CH-101. Babarkot Oyster Collected from Babarkot (20°52'N, 71°25'E) at 8 m asl. CH-102. Diu Oyster Collected from Diu (20°44'N, 70°55'E) at 2 m asl. CH-103. Jafarabad Oyster Collected from Jafarabad (20°52'N, 71°25'E) at 3 m asl. CH-108. Rohisa Oyster Collected from Rohisa (20°50'N, 71°15'E) at 2 m asl.