The Arabian Sea covers only a small area of the world oceans, but has a significant influence on ... more The Arabian Sea covers only a small area of the world oceans, but has a significant influence on the global cycle of nitrogen. It is one of the three oceanic regions where a mid water oxygen minimum zone has been observed. Under hypoxic conditions the oxygen source used by bacteria to reduce organic matter is nitrate. This leads to the
Sedimentation in the ocean is fed by large aggregates produced in the surface mixed layer that si... more Sedimentation in the ocean is fed by large aggregates produced in the surface mixed layer that sink rapidly through the water column. These particles sampled by sediment traps have often been proposed to interact by disaggregation and scavenging with a pool of fine suspended matter with very slow sinking velocities and thus a long residence time. We investigated the amino acid composition and stable nitrogen isotopic ratios of suspended matter sampled during the late SW monsoon season in the Arabian Sea and compared them to those of sinking particles to investigate organic matter degradation/modification during passage through the water column. We found that amino acid (AA) composition of mixed layer suspended matter corresponds more to fresh plankton and their aggregates, whereas AA composition of suspended matter in the sub-thermocline water column deviated progressively from mixed layer composition. We conclude that suspended matter in deep waters and in the mixed layers of oligo...
Sedimentation in the ocean is fed by large aggregates produced in the surface mixed layer that si... more Sedimentation in the ocean is fed by large aggregates produced in the surface mixed layer that sink rapidly through the water column. These particles sampled by sediment traps have often been proposed to interact by disaggregation and scavenging with a pool of fine suspended matter with very slow sinking velocities and thus a long residence time. We investigated the amino acid (AA) composition and stable nitrogen isotopic ratios of suspended matter (SPM) sampled during the late SW monsoon season in the Arabian Sea and compared them to those of sinking particles to understand organic matter degradation/modification during passage through the water column. We found that AA composition of mixed layer suspended matter corresponds more to fresh plankton and their aggregates, whereas AA composition of SPM in the sub-thermocline water column deviated progressively from mixed layer composition. We conclude that suspended matter in deep waters and in the mixed layers of oligotrophic stations...
The Arabian Sea plays an important role in the marine nitrogen cycle because of its pronounced mi... more The Arabian Sea plays an important role in the marine nitrogen cycle because of its pronounced mid-water oxygen minimum zone (OMZ) in which bio-available nitrate (NO3-) is reduced to dinitrogen gas (N-2). As the nitrogen cycle can respond fast to climate-induced changes in productivity and circulation, the Arabian Sea sediments are an important palaeoclimatic archive. In order to understand seasonal and interannual variations in the nitrogen cycle, nutrient data were obtained from the literature published prior to 1993, evaluated, and compared with data measured during five expeditions carried out in the framework of the Joint Global Ocean Flux Study (JGOFS) in the Arabian Sea in 1995 and during a research cruise of RV Meteor in 2007. The data comparison showed that the area characterized by a pronounced secondary nitrite maximum (SNM) was by 63% larger in 1995 than a similarly determined estimate based on pre-JGOFS data. This area, referred to as the core of the denitrifying zone, ...
Investigations on surface sediments and a sediment core from Lake Lonar in central India were car... more Investigations on surface sediments and a sediment core from Lake Lonar in central India were carried out within the framework of the HIMPAC (Himalaya: Modern and Past Climate) programme. The aim was to understand recent productivity, sedimentation, and degradation processes and to reconstruct variations in Holocene lake conditions on the basis of biogeochemical analysis on a 10 m long sediment core retrieved from the centre of Lake Lonar. Located in India's core monsoon zone, Lake Lonar offers valuable information about the climate development of the whole region. The lake is situated at the floor of a meteorite impact structure on the Deccan plateau basalt. The modern lake is characterised by brackish water, high alkalinity, severe eutrophication, and bottom water anoxia. The lake is about 6 m deep and fed by rainfall during the SW monsoon season and three perennial streams. Since no out-flowing stream is present and no seepage loss occurs, the lake level is highly sensitive t...
The DFG funded HIMPAC (Himalaya: Modern and Past Climates) programme aims to reconstruct Holocene... more The DFG funded HIMPAC (Himalaya: Modern and Past Climates) programme aims to reconstruct Holocene Indian Monsoon climate using a multi-proxy and multi-archive approach. First investigations made on sediments from a ca. 10 m long core covering the whole Holocene taken from the lake Lonar in central India's state Maharashtra, Buldhana District, serve to identify changes in sedimentation, lake chemistry, local vegetation and regional to supra-regional climate patterns. Lake Lonar occupies the floor of an impact crater that formed on the ~ 65 Ma old basalt flows of the Deccan Traps. It covers an area of ca. 1 km2 and is situated in India's core monsoon area. The modern lake has a maximum depth of about 5 m, is highly alkaline, and hyposaline, grouped in the Na-Cl-CO3 subtype of saline lakes. No out-flowing stream is present and only three small streams feed the lake, resulting in a lake level highly sensitive to precipitation and evaporation. The lake is eutrophic and stratified...
We report the results of our investigations into the ca. 10m long core raised from the Lonar lake... more We report the results of our investigations into the ca. 10m long core raised from the Lonar lake, central India. This record represents the first complete reconstruction of the Indian monsoon variability from the core of the Indian monsoon in continental India. Lithological and geochemical changes clearly indicate the presence of an arid Younger Dryas event, a relatively wet phase ca. 11.5-6.4 cal ka. The timing of onset of the wet phase is coincident with Arabian Sea core records (Sirocko et al., 1993) but is much earlier than documented in the Oman stalagmites (Fleitmann et al., 2003). We find evidence of two prominent drier phases during the Holocene between 4.7-3.8 and 1.2-0.4 cal ka which are marked by the presence of the evaporitic mineral gaylussite. A clear evidence of an anthropogenic impact on organic producitivity is observed in the past 1200 years.
ABSTRACT High resolution isotopic (δ18O and δ13C) investigations on endogenic carbonates (calcite... more ABSTRACT High resolution isotopic (δ18O and δ13C) investigations on endogenic carbonates (calcite/aragonite) from Tso Moriri Lake, NW Himalaya show dramatic fluctuations during the late glacial and the early Holocene, and a persistent enrichment trend during the late Holocene. Changes in this lake are largely governed by the [input (meltwater+monsoon precipitation)/evaporation] (I/E) ratio, also reflected in changes in the carbonate mineralogy with aragonite being formed during periods of lowest I/E. Using new isotopic data on endogenic carbonates in combination with the available data on geochemistry, mineralogy, and reconstructed mean annual precipitation, we demonstrate that the late glacial and early Holocene carbonate δ18O variability resulted from fluctuating Indian summer monsoon (ISM) precipitation in NW Himalaya. This region experienced increasing ISM precipitation between ca. 13.1-11.7 cal ka and highest ISM precipitation during the early Holocene (11.2-8.5 cal ka). However, during the late Holocene, evaporation was the dominant control on the carbonate δ18O. Regional comparison of reconstructed hydrological changes from Tso Moriri Lake with other archives from the Asian summer monsoon and westerlies domain shows that the intensified westerly influence that resulted in higher lake levels (after 8 cal ka) in central Asia was not strongly felt in NW Himalaya.
The available data on Holocene climate variability from Asia indicates spatio-temporal changes in... more The available data on Holocene climate variability from Asia indicates spatio-temporal changes in the precipitation over this vast region. Detailed information on the timing, duration, regionality, and causes of these fluctuations is not well understood, especially over the Indian subcontinent. My work focuses on long core sediments from lake Tso Moriri (78°14'-78°25'N and 32°40'-33°02'E; altitude: 4500 m) situated in climatically sensitive zone of NW Himalayas affected by both mid-latitude westerlies and Indian summer monsoon. Two cores ca.7 m were retrieved from the lake at different water depths (ca. 40m and 105m) in July 2011. Investigations reveal marked changes in grain size, lamination quality, mineralogy, organic and carbonate content suggesting changes in lake level, direction of inflow, and biological productivity that in turn are influenced by regional climate. As the lake lies in a tectonically active region, I have also undertaken detailed geomorphometri...
Understanding the variability of Indian Summer Monsoon activity and the influences of different c... more Understanding the variability of Indian Summer Monsoon activity and the influences of different climatic forcing factors on the monsoon strength is of high importance because of the crucial effect of monsoonal rainfall for the largely agricultural based south Asian societies. The discovery of the weakening relationship between El Niño Southern Oscillation (ENSO) and the Indian Summer Monsoon rainfall (ISM) in recent decades has raised the question about the ISM-ENSO links during the Holocene. Long term high resolution palaeoclimate data from central India, the so called "core monsoon region", can help to address this issue. Here we present the first well dated 11.5 cal ka high resolution multi-proxy record from Lonar lake, central India. Lithology, evaporites, stable isotopes, and palynological data, suggest generally moist conditions in the early to mid-Holocene, followed by a trend towards more arid conditions that started between 4.7 and 4.2cal ka BP. Moreover, we ident...
The Arabian Sea covers only a small area of the world oceans, but has a significant influence on ... more The Arabian Sea covers only a small area of the world oceans, but has a significant influence on the global cycle of nitrogen. It is one of the three oceanic regions where a mid water oxygen minimum zone has been observed. Under hypoxic conditions the oxygen source used by bacteria to reduce organic matter is nitrate. This leads to the
Sedimentation in the ocean is fed by large aggregates produced in the surface mixed layer that si... more Sedimentation in the ocean is fed by large aggregates produced in the surface mixed layer that sink rapidly through the water column. These particles sampled by sediment traps have often been proposed to interact by disaggregation and scavenging with a pool of fine suspended matter with very slow sinking velocities and thus a long residence time. We investigated the amino acid composition and stable nitrogen isotopic ratios of suspended matter sampled during the late SW monsoon season in the Arabian Sea and compared them to those of sinking particles to investigate organic matter degradation/modification during passage through the water column. We found that amino acid (AA) composition of mixed layer suspended matter corresponds more to fresh plankton and their aggregates, whereas AA composition of suspended matter in the sub-thermocline water column deviated progressively from mixed layer composition. We conclude that suspended matter in deep waters and in the mixed layers of oligo...
Sedimentation in the ocean is fed by large aggregates produced in the surface mixed layer that si... more Sedimentation in the ocean is fed by large aggregates produced in the surface mixed layer that sink rapidly through the water column. These particles sampled by sediment traps have often been proposed to interact by disaggregation and scavenging with a pool of fine suspended matter with very slow sinking velocities and thus a long residence time. We investigated the amino acid (AA) composition and stable nitrogen isotopic ratios of suspended matter (SPM) sampled during the late SW monsoon season in the Arabian Sea and compared them to those of sinking particles to understand organic matter degradation/modification during passage through the water column. We found that AA composition of mixed layer suspended matter corresponds more to fresh plankton and their aggregates, whereas AA composition of SPM in the sub-thermocline water column deviated progressively from mixed layer composition. We conclude that suspended matter in deep waters and in the mixed layers of oligotrophic stations...
The Arabian Sea plays an important role in the marine nitrogen cycle because of its pronounced mi... more The Arabian Sea plays an important role in the marine nitrogen cycle because of its pronounced mid-water oxygen minimum zone (OMZ) in which bio-available nitrate (NO3-) is reduced to dinitrogen gas (N-2). As the nitrogen cycle can respond fast to climate-induced changes in productivity and circulation, the Arabian Sea sediments are an important palaeoclimatic archive. In order to understand seasonal and interannual variations in the nitrogen cycle, nutrient data were obtained from the literature published prior to 1993, evaluated, and compared with data measured during five expeditions carried out in the framework of the Joint Global Ocean Flux Study (JGOFS) in the Arabian Sea in 1995 and during a research cruise of RV Meteor in 2007. The data comparison showed that the area characterized by a pronounced secondary nitrite maximum (SNM) was by 63% larger in 1995 than a similarly determined estimate based on pre-JGOFS data. This area, referred to as the core of the denitrifying zone, ...
Investigations on surface sediments and a sediment core from Lake Lonar in central India were car... more Investigations on surface sediments and a sediment core from Lake Lonar in central India were carried out within the framework of the HIMPAC (Himalaya: Modern and Past Climate) programme. The aim was to understand recent productivity, sedimentation, and degradation processes and to reconstruct variations in Holocene lake conditions on the basis of biogeochemical analysis on a 10 m long sediment core retrieved from the centre of Lake Lonar. Located in India's core monsoon zone, Lake Lonar offers valuable information about the climate development of the whole region. The lake is situated at the floor of a meteorite impact structure on the Deccan plateau basalt. The modern lake is characterised by brackish water, high alkalinity, severe eutrophication, and bottom water anoxia. The lake is about 6 m deep and fed by rainfall during the SW monsoon season and three perennial streams. Since no out-flowing stream is present and no seepage loss occurs, the lake level is highly sensitive t...
The DFG funded HIMPAC (Himalaya: Modern and Past Climates) programme aims to reconstruct Holocene... more The DFG funded HIMPAC (Himalaya: Modern and Past Climates) programme aims to reconstruct Holocene Indian Monsoon climate using a multi-proxy and multi-archive approach. First investigations made on sediments from a ca. 10 m long core covering the whole Holocene taken from the lake Lonar in central India's state Maharashtra, Buldhana District, serve to identify changes in sedimentation, lake chemistry, local vegetation and regional to supra-regional climate patterns. Lake Lonar occupies the floor of an impact crater that formed on the ~ 65 Ma old basalt flows of the Deccan Traps. It covers an area of ca. 1 km2 and is situated in India's core monsoon area. The modern lake has a maximum depth of about 5 m, is highly alkaline, and hyposaline, grouped in the Na-Cl-CO3 subtype of saline lakes. No out-flowing stream is present and only three small streams feed the lake, resulting in a lake level highly sensitive to precipitation and evaporation. The lake is eutrophic and stratified...
We report the results of our investigations into the ca. 10m long core raised from the Lonar lake... more We report the results of our investigations into the ca. 10m long core raised from the Lonar lake, central India. This record represents the first complete reconstruction of the Indian monsoon variability from the core of the Indian monsoon in continental India. Lithological and geochemical changes clearly indicate the presence of an arid Younger Dryas event, a relatively wet phase ca. 11.5-6.4 cal ka. The timing of onset of the wet phase is coincident with Arabian Sea core records (Sirocko et al., 1993) but is much earlier than documented in the Oman stalagmites (Fleitmann et al., 2003). We find evidence of two prominent drier phases during the Holocene between 4.7-3.8 and 1.2-0.4 cal ka which are marked by the presence of the evaporitic mineral gaylussite. A clear evidence of an anthropogenic impact on organic producitivity is observed in the past 1200 years.
ABSTRACT High resolution isotopic (δ18O and δ13C) investigations on endogenic carbonates (calcite... more ABSTRACT High resolution isotopic (δ18O and δ13C) investigations on endogenic carbonates (calcite/aragonite) from Tso Moriri Lake, NW Himalaya show dramatic fluctuations during the late glacial and the early Holocene, and a persistent enrichment trend during the late Holocene. Changes in this lake are largely governed by the [input (meltwater+monsoon precipitation)/evaporation] (I/E) ratio, also reflected in changes in the carbonate mineralogy with aragonite being formed during periods of lowest I/E. Using new isotopic data on endogenic carbonates in combination with the available data on geochemistry, mineralogy, and reconstructed mean annual precipitation, we demonstrate that the late glacial and early Holocene carbonate δ18O variability resulted from fluctuating Indian summer monsoon (ISM) precipitation in NW Himalaya. This region experienced increasing ISM precipitation between ca. 13.1-11.7 cal ka and highest ISM precipitation during the early Holocene (11.2-8.5 cal ka). However, during the late Holocene, evaporation was the dominant control on the carbonate δ18O. Regional comparison of reconstructed hydrological changes from Tso Moriri Lake with other archives from the Asian summer monsoon and westerlies domain shows that the intensified westerly influence that resulted in higher lake levels (after 8 cal ka) in central Asia was not strongly felt in NW Himalaya.
The available data on Holocene climate variability from Asia indicates spatio-temporal changes in... more The available data on Holocene climate variability from Asia indicates spatio-temporal changes in the precipitation over this vast region. Detailed information on the timing, duration, regionality, and causes of these fluctuations is not well understood, especially over the Indian subcontinent. My work focuses on long core sediments from lake Tso Moriri (78°14'-78°25'N and 32°40'-33°02'E; altitude: 4500 m) situated in climatically sensitive zone of NW Himalayas affected by both mid-latitude westerlies and Indian summer monsoon. Two cores ca.7 m were retrieved from the lake at different water depths (ca. 40m and 105m) in July 2011. Investigations reveal marked changes in grain size, lamination quality, mineralogy, organic and carbonate content suggesting changes in lake level, direction of inflow, and biological productivity that in turn are influenced by regional climate. As the lake lies in a tectonically active region, I have also undertaken detailed geomorphometri...
Understanding the variability of Indian Summer Monsoon activity and the influences of different c... more Understanding the variability of Indian Summer Monsoon activity and the influences of different climatic forcing factors on the monsoon strength is of high importance because of the crucial effect of monsoonal rainfall for the largely agricultural based south Asian societies. The discovery of the weakening relationship between El Niño Southern Oscillation (ENSO) and the Indian Summer Monsoon rainfall (ISM) in recent decades has raised the question about the ISM-ENSO links during the Holocene. Long term high resolution palaeoclimate data from central India, the so called "core monsoon region", can help to address this issue. Here we present the first well dated 11.5 cal ka high resolution multi-proxy record from Lonar lake, central India. Lithology, evaporites, stable isotopes, and palynological data, suggest generally moist conditions in the early to mid-Holocene, followed by a trend towards more arid conditions that started between 4.7 and 4.2cal ka BP. Moreover, we ident...
Uploads
Papers by Birgit Gaye