Description: Sedimentary d15N records are valuable archives of ocean history but they are often modified during early diagenesis. Here we quantify the effect of early diagenetic enrichment on sedimentary N-isotope composition in order to obtain the pristine signal of reactive N assimilated in the euphotic zone. This is possible by using paired data of d15N and amino acid composition of sediment samples, which can be applied to estimate the degree of organic matter degradation. We determined d15N and amino acid composition in coeval sediments from Ocean Drilling Program (ODP) Hole 772 B in the central Arabian Sea and from Hole 724 C situated on the Oman Margin in the western Arabian Sea coastal upwelling area. The records span the last 130 kyr and include two glacial-interglacial cycles. These new data are used in conjunction with data available for surface sediments that cover a wide range of organic matter degradation states, and with other cores from the northern and eastern Arabian Sea to explore spatial variations in the isotopic signal. In order to reconstruct pristine N values we apply the relationship between organic matter degradation and 15N enrichment in surface sediments to correct the core records for early diagenetic enrichment. Reconstructed d15N values suggest a significant role of N2-fixation during glacial stages. An evaluation of two preservation indices based on amino acid composition (Reactivity Index, RI; Jennerjahn and Ittekkot, 1997; and the Degradation Index, DI; Dauwe et al., 1999) in both recent sediments and core samples suggests that the RI is more suitable than the DI in correcting Arabian Sea d15N records for early diagenetic enrichment.

Description: Variability in the oceanic environment of the Arabian Sea region is strongly influenced by the seasonal monsoon cycle of alternating wind directions. Prominent and well studied is the summer monsoon, but much less is known about late Holocene changes in winter monsoon strength with winds from the northeast that drive convective mixing and high surface ocean productivity in the northeastern Arabian Sea. To establish a high-resolution record of winter monsoon variability for the late Holocene, we analyzed alkenone-derived sea surface temperature (SST) variations and proxies of primary productivity (organic carbon and d15N) in a well-laminated sediment core from the Pakistan continental margin. Weak winter monsoon intensities off Pakistan are indicated from 400 B.C. to 250 A.D. by reduced productivity and relatively high SST. At about 250 A.D., the intensity of the winter monsoon increased off Pakistan as indicated by a trend to lower SST. We infer that monsoon conditions were relatively unstable from ~500 to 1300 A.D., because primary production and SST were highly variable. Declining SST and elevated biological production from 1400 to 1900 A.D. suggest invigorated convective winter mixing by strengthening winter monsoon circulation, most likely a regional expression of colder climate conditions during the Little Ice Age on the Northern Hemisphere. The comparison of winter monsoon intensity with records of summer monsoon intensity suggests that an inverse relationship between summer and winter monsoon strength exists in the Asian monsoon system during the late Holocene, effected by shifts in the Intertropical Convergence Zone.

Description: In the present study, we report the results of comprehensive amino acid (AA) analyses of four Indian lakes from different climate regimes. We focus on the investigation of sediment cores retrieved from the lakes but data of modern sediment as well as vascular plant, soil, and suspended particulate matter samples from individual lakes are also presented. Commonly used degradation and organic matter source indices are tested for their applicability to the lake sediments, and we discuss potential reasons for possible limitations. A principal component analysis including the monomeric AA composition of organic matter of all analysed samples indicates that differences in organic matter sources and the environmental properties of the individual lakes are responsible for the major variability in monomeric AA distribution of the different samples. However, the PCA also gives a factor that most probably separates the samples according to their state of organic matter degradation. Using the factor loadings of the individual AA monomers, we calculate a lake sediment degradation index (LI) that might be applicable to other palaeo-lake investigations.

Description: The sediment trap experiment started in 1986 and was expanded into the Bay of Bengal only one year later in 1987. The fieldwork ended at around 1998. In 2007 and 2008, we tried to reinitiate a sediment trap program in the Arabian Sea, although this could not be followed up due to piracy, which became an issue in the region at that time. The sediment trap sites in the northern and central Bay of Bengal were shifted slightly southward in some years, whereby the stations NBBT and CBBT were spilt into northern (NBBT-N, CBBT-N) and southern sites (NBBT-S, CBBT-S). Between 2001 and 2004 additional sediment trap experiments were carried out in the upwelling system off South Java.

Description: ICP-OES and ICP-MS data of trace elements in sediment and pore waters of the DISCOL area, Peru Basin, SE Pacific

Description: Laminated sediments of the continental slope off the Makran coast in the northern Arabian Sea are well-known climate archives and record productivity as well as supply of material from land. Here we studied sediment core 275KL off Pakistan in concert with sediment trap, dust and river samples in order to characterise and quantify land-derived material deposited in varves and event layers. We analysed grain sizes, mineral assemblages, bulk components, and stable isotopes (δ13C, δ18O) of carbonates. In winter, enhanced river discharge is the main source of lithogenic matter contributing the major amounts to the total annual sedimentation of the northern Arabian Sea. During the late summer season, lithogenic matter accumulation is slightly enhanced, probably carried along with the southeastward blowing Levar winds from the Balochistan and the Sistan Basins and the summer monsoon discharge maximum of perennial streams. C/N ratios and stable carbon and oxygen isotopes could not be used to distinguish between organic matter produced on land and in the ocean, whereas stable carbon and oxygen isotope ratios of carbonates suggest that sedimentation of event layers is dominated by direct inputs from land. Catastrophic denudation and storm events occur on average once every 50 years and lead to sedimentation rates that exceed the mean annual sedimentations of 983 g m-2 yr-1 by 6 to 10 times. Nevertheless, due to their rare occurrence they contributed only 7% to the total sedimentation during the last ca 5,000 years. End-member modelling of grain sizes in accordance with lithogenic matter accumulation rates and event layer frequencies showed that arid conditions prevailed between 4,000 and 5,000 a BP while more humid conditions commenced around 2,000 ka BP in accordance with the Pacific ENSO record.

Description: At present the Arabian Sea has a permanent oxygen minimum zone (OMZ) at water depths between about 100 m and 1200 m. Active denitrification in this OMZ is recorded by enhanced d15N values in the sediments. Sediment cores show a d15N increase from early to late Holocene which is contrary to the trend in other regions of water column denitrification. We calculated composite sea surface temperature (SST) and d15N in time slices of 1000 years of the last 25 ka to better understand the reasons for the establishment of the Arabian Sea OMZ and its response to changes in the Asian monsoon system. Pleistocene stadial d15N values of 4-6 per mil suggest that denitrification was inactive or weak. During interstadials (IS) and the entire Holocene, d15N values of 〉7 per mil indicate enhanced denitrification and a stronger OMZ. This coincides with active monsoonal upwelling along the western margins of the basin as indicated by low SST. Stronger ventilation of the OMZ in the early to mid-Holocene period during the most intense southwest monsoon and vigorous upwelling is reflected in lower d15N compared to the late Holocene. The displacement of the core of the OMZ from the region of maximum productivity in the western Arabian Sea to its present position in the northeast was established during the last 4-5 ka. This was probably caused by (i) rising oxygen consumption due to enhanced northeast monsoon driven biological productivity, in combination with (ii) reduced ventilation due to a longer residence time of OMZ waters.

Description: The Indian Summer Monsoon (ISM) with its rainfall is the lifeline for people living on the Indian subcontinent today and possibly was the driver of the rise and fall of early agricultural societies in the past. Intensity and position of the ISM have shifted in response to orbitally forced thermal land-ocean contrasts. At the northwestern monsoon margins, interactions between the subtropical westerly jet (STWJ) and the ISM constitute a tipping element in the Earth's climate system, because their non-linear interaction may be a first-order influence on rainfall. We reconstructed marine sea surface temperature (SST), supply of terrestrial material and vegetation changes from a very well-dated sediment core from the northern Arabian Sea to reconstruct the STWJ-ISM interaction. The Holocene record (from 11,000 years) shows a distinct, but gradual, southward displacement of the ISM in the Early to Mid-Holocene, increasingly punctuated by phases of intensified STWJ events that are coeval with interruptions of North Atlantic overturning circulation (Bond events). Effects of the non-linear interactions culminate between 4.6-3 ka BP, marking a climatic transition period during which the ISM shifted southwards and the influence of SWTJ became prominent. The lithogenic input shows an up to 4-fold increase after this time period signaling the strengthened influence of agricultural activities of the Indus civilization with enhanced erosion of soils amplifying the impact of Bond events and adding to the marine sedimentation rates adjacent to the continent.

Description: The Indian Monsoon and the westerlies strongly influence the sedimentation in the northeastern Arabian Sea by impacting rainfall and erosion on land and on biogeochemical processes in the ocean. To disentangle the terrestrial and oceanic processes, we analysed mineralogical and bulk geochemical components of a Holocene sediment core offshore Pakistan. Endmember modelling of grain sizes and principal component analyses (PCA) of major and trace elements identify the origin of sediments and their dominant mode of transport. Sedimentation processes during the early Holocene (10.8–8.2 ka BP) were influenced by the post-glacial sea level rise and orbitally forced strengthening of the Indian summer monsoon (ISM) and westerlies. This led to a shift from rather terrestrial-dominated towards a marine-dominated sedimentation, whereas the fluvial source shifted from the Makran rivers to the Hab River near Karachi. During the mid-Holocene (8.2–4.2 ka BP) a combination of weakening ISM and southward displacement of the ITCZ enhanced the influence of the westerlies, together decreasing river discharges and enhancing aeolian input (probably from the Sistan Basin region). This trend continued during the last ca. 4 ka when the increasing aridification of the Hab River catchment further increased the aeolian inputs. Solar and lunar driven short-term variations as well as Bond events known from the North Atlantic Ocean superpose these trends. They lead to a pronounced increase of fluvial inputs between 8.6–8.4 ka BP and at ca. 3 ka BP as well as to dry events around 4.2 ka and 1.2–1 ka BP. Our study highlights the increasing influence of the westerlies on the sedimentation processes in the northeastern Arabian Sea towards the late Holocene.

Description: The data sets contains the age model as well as bulk organic and n-alkane data of sediment core GeoTü SL167 to reconstruct changes of the oxygen minimum zone strength for the late Quaternary. The age model is based on 14C AMS measurements of planktonic foraminifera and is calibrated with the BACON v. 2.5.6 software for R (Blauuw & Christen, 2011) and a marine reservoir age of ΔR = 93 ± 61 years. The ΔR is based on the weighted mean of two regional marine reservoir corrections (Muscat) by Southon et al. (2002) using the marine calibration database (Reimer and Reimer, 2001, http://calib.org/marine/). Total organic carbon and nitrogen measurements were carried out with an Euro EA3000 elemental analyser and δ15N measurements with a Thermo Scientific Flash EA1112 coupled to a Finnigan MAT 252 IRMS. Total organic carbon mass accumulation rates (TOC MAR) based on calculation using the organic carbon content and total mass accumulation rates. A description of the calculation of the total mass accumulations rates is given in Burdanowitz et al 2021. The measurements of n-alkanes were carried out using Thermo Scientific Trace 1310 GC-FID and Thermo Scientific DSQ II (GC-MS). Gravity core GeoTü SL167, was retrieved at station no. 960 during R.V. METEOR cruise M74/1b in 2007 (Bohrmann et al., 2010) from the northwestern Arabian Sea off Oman, at 22°37.2'N, 59°41.5'E, 774 m water depth, core recovery 7.39 m. The sediment core was retrieved for the reconstruction of circulation and productivity changes in the eastern Mediterranean Sea during the late Quaternary with particular focus on changes in the Indian monsoon system.