[1] Nitrogen isotopes are an important tool for evaluating past biogeochemical cycling from the paleoceanographic record. However, bulk sedimentary nitrogen isotope ratios, which can be determined routinely and at minimal cost, may be altered during burial and early sedimentary diagenesis, particularly outside of continental margin settings. The causes and detailed mechanisms of isotopic alteration are still under investigation. Case studies of the Mediterranean and South China Seas underscore the complexities of investigating isotopic alteration. In an effort to evaluate the evidence for alteration of the sedimentary N isotopic signal and try to quantify the net effect, we have compiled and compared data demonstrating alteration from the published literature. A >100 point comparison of sediment trap and surface sedimentary nitrogen isotope values demonstrates that, at sites located off of the continental margins, an increase in sediment 15 N/ 14 N occurs during early burial, likely at the seafloor. The extent of isotopic alteration appears to be a function of water depth. Depth-related differences in oxygen exposure time at the seafloor are likely the dominant control on the extent of N isotopic alteration. Moreover, the compiled data suggest that the degree of alteration is likely to be uniform through time at most sites so that bulk sedimentary isotope records likely provide a good means for evaluating relative changes in the global N cycle.Citation: Robinson, R. S., et al. (2012), A review of nitrogen isotopic alteration in marine sediments, Paleoceanography, 27, PA4203,

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[1] Sediment cores from Ocean Drilling Program sites 1094 and 1093 hold the most extensive and most detailed records of carbon and nitrogen isotopes of diatom-bound organic matter in the Atlantic sector of the Southern Ocean over the past 660 ka. These records were combined with summer sea surface temperatures and winter sea ice that were deduced from diatom transfer functions to reconstruct the nutrient regime at the northern and southern boundaries of the siliceous belt at latitudes 53°S and 50°S, respectively. The strong coupling between carbon and nitrogen isotope records at site 1093 suggests that the diatom productivity was influenced mainly by changes in nutrient availability. The anticorrelation between the carbon and nitrogen isotopes at site 1094 suggests that the diatom productivity was closely linked to global temperature changes, sea ice coverage, and dissolved CO 2 concentration. A detailed comparison of the nitrogen isotope records between the two sites shows three time intervals that represent different nutrient regimes. The nutrients at site 1093, which is close to the Polar Front, were dominated by eddies and meanders that sustained relatively high productivity at times of stratification or reduced ventilation, whereas at site 1094 the nutrients were influenced by ventilation processes.Citation: Schneider-Mor, A., R. Yam, C. Bianchi, M. Kunz-Pirrung, R. Gersonde, and A. Shemesh (2008), Nutrient regime at the siliceous belt of the Atlantic sector of the Southern Ocean during the past 660 ka, Paleoceanography, 23, PA3217,

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[1] The flux of sediment and organic carbon from continents to the coastal ocean is an important factor governing organic burial in coastal sediments, and these systems preserve important records of environmental and biogeochemical conditions during past global change events. Burial of organic materials in coastal systems can be promoted by chemical resilience or through protection by association with mineral surfaces, but the role and influence of these processes on organic records from ancient sediments is poorly known. We studied sediment and organic matter burial as particulate organic matter (POM) and mineral-bound organic matter (MOM) in near-shore marine sediments from the Wilson Lake core (New Jersey, USA) that span the Paleocene-Eocene thermal maximum (PETM), a climatic perturbation 55.9 Myr ago. Our results show that distinct POM and MOM fractions can be isolated from sediments. Both fractions appear to be dominated by terrestrial material, but POM consisted primarily of recently synthesized material whereas MOM included a significant fraction of pre-aged organic matter from soils or ancient sediments. Variation in organic burial through the PETM is associated with changes in inorganic nitrogen burial, clay mineralogy, and clastic grain size that we associate with enhanced continental weathering, erosion and redeposition of ancient kaolinites, and eustatic sea level variation, respectively. These results provide a new perspective on factors governing carbon burial and carbon isotope records in ancient marine margin settings and offer information on rate and phasing of late Paleocene/early Eocene Earth system changes that may constrain interpretations of the cause of the PETM climate change event.Citation: Schneider-Mor, A., and G. J. Bowen (2013), Coupled and decoupled responses of continental and marine organic-sedimentary systems through the Paleocene-Eocene thermal maximum, New Jersey margin, USA, Paleoceanography, 28, 105-115,

The River Nile catchment is considered the major source of nutrient-rich freshwater and sediment draining into the eastern Mediterranean Sea. Thus, exceptional high-resolution record from the Nile Littoral Cell likely traces changes in the Nile outflows related to climatic changes driven by the monsoonal system. This study used multi-proxy analyses combining sedimentological, geochemical and organic stable isotope data along with foraminiferal data in a southeastern Levantine inner shelf sedimentary sequence to understand Mid-to Late Holocene northeast African climate variability. The palynological record is used to reconstruct local scale changes in the regional vegetation related to the Mediterranean climate system. The analyzed records reveal multi-decadal to centennial pacing of paleoceanographic and paleoclimatic changes, with most prominent events recorded at 4.28,~3.6 and at 2.9 kyr BP. These transitional periods characterized by simultaneous high d 15 N values and low total organic carbon (TOC) suggest drier climatic conditions, decrease in Nile discharge, leading to lower nutrient supply. A stable and arid climate during Mid-Late Holocene (~4.5e3.6 cal kyr BP) associated with a weaker monsoon system as well as with a weaker Mediterranean climate system is indicated based on high and constant sedimentation rates (~400 cm kyr À1), along with relatively stable values and only occasional weak fluctuations documented in all of the proxies. This climatic pattern is punctuated by a peak in maximum aridity at 4.28 kyr BP evidenced by low TOC value and low arboreal pollen (AP) and Artemisia/Chenopodiaceae (A/C) pollen ratios and the sharp decline in the abundance of benthic foraminifera Cribroelphidium poeyanum and Valvulineria bradyana. This change corresponds with the wellstudied 4.2 kyr BP drought event in the Middle East, Mesopotamia and south Asia. During the late Holocene (~3.6e2.8 cal. Kyr BP) the climate became unstable characterized by shifts between relatively wetter and drier conditions as evident in considerable fluctuations in all proxies. Maximum positive excursions of TOC values, C/N ratio along with high dominance of opportunistic foraminiferal species (e.g., Ammonia tepida) indicate northeast African wetter conditions and increased Nile discharge at 3.5, 3.3, 3.2 and 3.0 kyr BP. The distinct and abrupt transition from a stable to an unstable climate regime around 3.6 kyr BP may have been influenced by the Thera volcanic eruption. Thus, the sedimentary record investigated in this study may provide evidence for the impacts of this wellknown volcanic eruption not just on the climate regime in the Levant but also on the ancient Near East and Egypt.