@article{DeplazesLueckgeStuutetal.2014, author = {Deplazes, Gaudenz and L{\"u}ckge, Andreas and Stuut, Jan-Berend W. and Paetzold, J{\"u}rgen and Kuhlmann, Holger and Husson, Dorothee and Fant, Mara and Haug, Gerald H.}, title = {Weakening and strengthening of the Indian monsoon during Heinrich events and Dansgaard- Oeschger oscillations}, series = {Paleoceanography}, volume = {29}, journal = {Paleoceanography}, number = {2}, publisher = {American Geophysical Union}, address = {Washington}, issn = {0883-8305}, doi = {10.1002/2013PA002509}, pages = {99 -- 114}, year = {2014}, abstract = {The Dansgaard-Oeschger oscillations and Heinrich events described in North Atlantic sediments and Greenland ice are expressed in the climate of the tropics, for example, as documented in Arabian Sea sediments. Given the strength of this teleconnection, we seek to reconstruct its range of environmental impacts. We present geochemical and sedimentological data from core SO130-289KL from the Indus submarine slope spanning the last similar to 80 kyr. Elemental and grain size analyses consistently indicate that interstadials are characterized by an increased contribution of fluvial suspension from the Indus River. In contrast, stadials are characterized by an increased contribution of aeolian dust from the Arabian Peninsula. Decadal-scale shifts at climate transitions, such as onsets of interstadials, were coeval with changes in productivity-related proxies. Heinrich events stand out as especially dry and dusty events, indicating a dramatically weakened Indian summer monsoon, potentially increased winter monsoon circulation, and increased aridity on the Arabian Peninsula. This finding is consistent with other paleoclimate evidence for continental aridity in the northern tropics during these events. Our results strengthen the evidence that circum-North Atlantic temperature variations translate to hydrological shifts in the tropics, with major impacts on regional environmental conditions such as rainfall, river discharge, aeolian dust transport, and ocean margin anoxia.}, language = {en} } @article{SernoWincklerAndersonetal.2014, author = {Serno, Sascha and Winckler, Gisela and Anderson, Robert F. and Hayes, Christopher T. and Ren, Haojia and Gersonde, Rainer and Haug, Gerald H.}, title = {Using the natural spatial pattern of marine productivity in the Subarctic North Pacific to evaluate paleoproductivity proxies}, series = {Paleoceanography}, volume = {29}, journal = {Paleoceanography}, number = {5}, publisher = {American Geophysical Union}, address = {Washington}, issn = {0883-8305}, doi = {10.1002/2013PA002594}, pages = {438 -- 453}, year = {2014}, abstract = {Sedimentary proxies used to reconstruct marine productivity suffer from variable preservation and are sensitive to factors other than productivity. Therefore, proxy calibration is warranted. Here we map the spatial patterns of two paleoproductivity proxies, biogenic opal and barium fluxes, from a set of core-top sediments recovered in the Subarctic North Pacific. Comparisons of the proxy data with independent estimates of primary and export production, surface water macronutrient concentrations, and biological pCO(2) drawdown indicate that neither proxy shows a significant correlation with primary or export productivity for the entire region. Biogenic opal fluxes, when corrected for preservation using Th-230-normalized accumulation rates, show a good correlation with primary productivity along the volcanic arcs (tau = 0.71, p = 0.0024) and with export productivity throughout the western Subarctic North Pacific (tau = 0.71, p = 0.0107). Moderate and good correlations of biogenic barium flux with export production (tau = 0.57, p = 0.0022) and with surface water silicate concentrations (tau = 0.70, p = 0.0002) are observed for the central and eastern Subarctic North Pacific. For reasons unknown, however, no correlation is found in the western Subarctic North Pacific between biogenic barium flux and the reference data. Nonetheless, we show that barite saturation, uncertainty in the lithogenic barium corrections, and problems with the reference data sets are not responsible for the lack of a significant correlation between biogenic barium flux and the reference data. Further studies evaluating the factors controlling the variability of the biogenic constituents in the sediments are desirable in this region.}, language = {en} } @article{LechleitnerBreitenbachRehfeldetal.2017, author = {Lechleitner, Franziska A. and Breitenbach, Sebastian Franz Martin and Rehfeld, Kira and Ridley, Harriet E. and Asmerom, Yemane and Prufer, Keith M. and Marwan, Norbert and Goswami, Bedartha and Kennett, Douglas J. and Aquino, Valorie V. and Polyak, Victor and Haug, Gerald H. and Eglinton, Timothy I. and Baldini, James U. L.}, title = {Tropical rainfall over the last two millennia: evidence for a low-latitude hydrologic seesaw}, series = {Scientific reports}, volume = {7}, journal = {Scientific reports}, publisher = {Nature Publ. Group}, address = {London}, issn = {2045-2322}, doi = {10.1038/srep45809}, pages = {9}, year = {2017}, abstract = {The presence of a low-to mid-latitude interhemispheric hydrologic seesaw is apparent over orbital and glacial-interglacial timescales, but its existence over the most recent past remains unclear. Here we investigate, based on climate proxy reconstructions from both hemispheres, the inter-hemispherical phasing of the Intertropical Convergence Zone (ITCZ) and the low-to mid-latitude teleconnections in the Northern Hemisphere over the past 2000 years. A clear feature is a persistent southward shift of the ITCZ during the Little Ice Age until the beginning of the 19th Century. Strong covariation between our new composite ITCZ-stack and North Atlantic Oscillation (NAO) records reveals a tight coupling between these two synoptic weather and climate phenomena over decadal-to-centennial timescales. This relationship becomes most apparent when comparing two precisely dated, high-resolution paleorainfall records from Belize and Scotland, indicating that the low-to mid-latitude teleconnection was also active over annual-decadal timescales. It is likely a combination of external forcing, i.e., solar and volcanic, and internal feedbacks, that drives the synchronous ITCZ and NAO shifts via energy flux perturbations in the tropics.}, language = {en} } @article{SigmanHainHaug2010, author = {Sigman, Daniel M. and Hain, Mathis P. and Haug, Gerald H.}, title = {The polar ocean and glacial cycles in atmospheric CO2 concentration}, issn = {0028-0836}, doi = {10.1038/Nature09149}, year = {2010}, abstract = {Global climate and the atmospheric partial pressure of carbon dioxide (p(CO2atm)) are correlated over recent glacial cycles, with lower p(CO2atm) during ice ages, but the causes of the p(CO2atm) changes are unknown. The modern Southern Ocean releases deeply sequestered CO2 to the atmosphere. Growing evidence suggests that the Southern Ocean CO2 'leak' was stemmed during ice ages, increasing ocean CO2 storage. Such a change would also have made the global ocean more alkaline, driving additional ocean CO2 uptake. This explanation for lower ice-age p(CO2atm), if correct, has much to teach us about the controls on current ocean processes.}, language = {en} } @article{JaccardGalbraithSigmanetal.2009, author = {Jaccard, Samuel Laurent and Galbraith, Eric D. and Sigman, Daniel M. and Haug, Gerald H. and Francois, Roger and Pedersen, Thomas F. and Dulski, Peter and Thierstein, Hans R.}, title = {Subarctic Pacific evidence for a glacial deepening of the oceanic respired carbon pool}, issn = {0012-821X}, doi = {10.1016/j.epsl.2008.10.017}, year = {2009}, abstract = {Measurements of benthic foraminiferal cadmium:calcium (Cd/Ca) have indicated that the glacial-interglacial change in deep North Pacific phosphate (PO4) concentration was minimal which has been taken by some, workers as a sign that the biological pump did not store more carbon in the deep glacial ocean. Here we present sedimentary redox- sensitive trace metal records from Ocean Drilling Program (ODP) Site 882 (NW subarctic Pacific, water depth 3244 m) to make inferences about changes in deep North Pacific oxygenation and thus respired carbon storage - over the past 150,000 yr. These observations are complemented with biogenic barium and opal measurements as indicators for past organic carbon export to separate the influences of deep-water oxygen concentration and sedimentary organic carbon respiration on the redox state of the sediment. Our results suggest that the deep subarctic Pacific water mass was deleted in ox en during glacial maxima, though it was not anoxic. We reconcile our results with the existing benthic foraminiferal Cd/Ca by invoking a decrease in the fraction of the deep ocean nutrient inventory that was preformed, rather than remineralized. This change would have corresponded to an increase in the deep Pacific storage of respired carbon, which Would have lowered atmospheric carbon dioxide (CO2) by sequestering CO2 away from the atmosphere and by increasing ocean alkalinity through a transient dissolution event in the deep sea. The magnitude of change in preformed nutrients suggested by the North Pacific data Would have accounted for a majority of the observed decrease in glacial atmospheric PCO2.}, language = {en} } @article{BreitenbachAdkinsMeyeretal.2010, author = {Breitenbach, Sebastian Franz Martin and Adkins, Jess F. and Meyer, Hanno and Marwan, Norbert and Kumar, Kanikicharla Krishna and Haug, Gerald H.}, title = {Strong influence of water vapor source dynamics on stable isotopes in precipitation observed in Southern Meghalaya, NE India}, issn = {0012-821X}, doi = {10.1016/j.epsl.2010.01.038}, year = {2010}, abstract = {To calibrate delta O-18 time-series from speleothems in the eastern Indian summer monsoon (ISM) region of India, and to understand the moisture regime over the northern Bay of Bengal (BoB) we analyze the delta O-18 and delta D of rainwater, collected in 2007 and 2008 near Cherrapunji, India. delta D values range from + 18.5 parts per thousand to 144.4 parts per thousand, while delta O-18 varies between +0.8 parts per thousand and 18.8 parts per thousand. The Local Meteoric Water Line (LMWL) is found to be indistinguishable from the Global Meteoric Water Line (GMWL). Late ISM (September-October) rainfall exhibits lowest delta O-18 and delta D values, with little relationship to the local precipitation amount. There is a trend to lighter isotope values over the course of the ISM, but it does not correlate with the patterns of temperature and rainfall amount delta O-18 and delta D time-series have to be interpreted with caution in terms of the 'amount effect' in this subtropical region. We find that the temporal trend in delta O-18 reflects increasing transport distance during the ISM, isotopic changes in the northern BoB surface waters during late ISM, and vapor re-equilibration with rain droplets. Using an isotope box model for surface ocean waters, we quantify the potential influence of river runoff on the isotopic composition of the seasonal freshwater plume in the northern BoB. Temporal variations in this source can contribute up to 25\% of the observed changes in stable isotopes of precipitation in NE India. To delineate other moisture sources, we use backward trajectory computations and find a strong correlation between source region and isotopic composition. Palaeoclimatic stable isotope time-series from northeast Indian speleothems likely reflect changes in moisture source and transport pathway, as well as the isotopic composition of the BoB surface water, all of which in turn reflect ISM strength. Stalagmite records from the region can therefore be interpreted as integrated measures of the ISM strength.}, language = {en} } @article{NaafsHefterActonetal.2012, author = {Naafs, B. David A. and Hefter, Jens and Acton, Gary and Haug, Gerald H. and Martinez-Garcia, Alfredo and Pancost, Richard and Stein, R{\"u}diger}, title = {Strengthening of North American dust sources during the late Pliocene (2.7 Ma)}, series = {Earth \& planetary science letters}, volume = {317}, journal = {Earth \& planetary science letters}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0012-821X}, doi = {10.1016/j.epsl.2011.11.026}, pages = {8 -- 19}, year = {2012}, abstract = {Here we present orbitally-resolved records of terrestrial higher plant leaf wax input to the North Atlantic over the last 3.5 Ma, based on the accumulation of long-chain n-alkanes and n-alkanl-1-ols at IODP Site U1313. These lipids are a major component of dust, even in remote ocean areas, and have a predominantly aeolian origin in distal marine sediments. Our results demonstrate that around 2.7 million years ago (Ma), coinciding with the intensification of the Northern Hemisphere glaciation (NHG), the aeolian input of terrestrial material to the North Atlantic increased drastically. Since then, during every glacial the aeolian input of higher plant material was up to 30 times higher than during interglacials. The close correspondence between aeolian input to the North Atlantic and other dust records indicates a globally uniform response of dust sources to Quaternary climate variability, although the amplitude of variation differs among areas. We argue that the increased aeolian input at Site U1313 during glacials is predominantly related to the episodic appearance of continental ice sheets in North America and the associated strengthening of glaciogenic dust sources. Evolutional spectral analyses of the n-alkane records were therefore used to determine the dominant astronomical forcing in North American ice sheet advances. These results demonstrate that during the early Pleistocene North American ice sheet dynamics responded predominantly to variations in obliquity (41 ka), which argues against previous suggestions of precession-related variations in Northern Hemisphere ice sheets during the early Pleistocene.}, language = {en} } @article{MartinezGarciaRosellMeleJaccardetal.2011, author = {Martinez-Garcia, Alfredo and Rosell-Mele, Antoni and Jaccard, Samuel L. and Geibert, Walter and Sigman, Daniel M. and Haug, Gerald H.}, title = {Southern Ocean dust-climate coupling over the past four million years}, series = {Nature : the international weekly journal of science}, volume = {476}, journal = {Nature : the international weekly journal of science}, number = {7360}, publisher = {Nature Publ. Group}, address = {London}, issn = {0028-0836}, doi = {10.1038/nature10310}, pages = {312 -- U141}, year = {2011}, abstract = {Dust has the potential to modify global climate by influencing the radiative balance of the atmosphere and by supplying iron and other essential limiting micronutrients to the ocean(1,2). Indeed, dust supply to the Southern Ocean increases during ice ages, and 'iron fertilization' of the subantarctic zone may have contributed up to 40 parts per million by volume (p. p. m. v.) of the decrease (80-100 p. p. m. v.) in atmospheric carbon dioxide observed during late Pleistocene glacial cycles(3-7). So far, however, the magnitude of Southern Ocean dust deposition in earlier times and its role in the development and evolution of Pleistocene glacial cycles have remained unclear. Here we report a high-resolution record of dust and iron supply to the Southern Ocean over the past four million years, derived from the analysis of marine sediments from ODP Site 1090, located in the Atlantic sector of the subantarctic zone. The close correspondence of our dust and iron deposition records with Antarctic ice core reconstructions of dust flux covering the past 800,000 years (refs 8, 9) indicates that both of these archives record large-scale deposition changes that should apply to most of the Southern Ocean, validating previous interpretations of the ice core data. The extension of the record beyond the interval covered by the Antarctic ice cores reveals that, in contrast to the relatively gradual intensification of glacial cycles over the past three million years, Southern Ocean dust and iron flux rose sharply at the Mid-Pleistocene climatic transition around 1.25 million years ago. This finding complements previous observations over late Pleistocene glacial cycles(5,8,9), providing new evidence of a tight connection between high dust input to the Southern Ocean and the emergence of the deep glaciations that characterize the past one million years of Earth history.}, language = {en} } @article{HainSigmanHaug2011, author = {Hain, Mathis P. and Sigman, Daniel M. and Haug, Gerald H.}, title = {Shortcomings of the isolated abyssal reservoir model for deglacial radiocarbon changes in the mid-depth Indo-Pacific Ocean}, series = {Geophysical research letters}, volume = {38}, journal = {Geophysical research letters}, number = {6}, publisher = {American Geophysical Union}, address = {Washington}, issn = {0094-8276}, doi = {10.1029/2010GL046158}, pages = {6}, year = {2011}, abstract = {Severely negative Delta(14)C anomalies from the mid-depth Pacific and the Arabian Sea have been taken as support for the hypothesized deglacial release of a previously isolated, extremely (14)C-deplete deep ocean carbon reservoir. We report box model simulations that cast doubt on both the existence of the hypothesized deep reservoir and its ability to explain the mid-depth Delta(14)C anomalies. First, the degree of ice age isolation needed to substantially reduce the deep Delta(14)C of the deep reservoir causes anoxia and the trapping of alkalinity from CaCO(3) dissolution, the latter increasing atmospheric CO(2). Second, even with a completely (14)C-free deep reservoir, achieving the mid-depth Delta(14)C anomalies of observed duration requires ad hoc stifling of aspects of deep circulation to prevent rapid dissipation of the anomalous (14)C-free carbon to the rest of the ocean and the atmosphere. We suggest that the mid-depth anomalies do not record basin-scale Delta(14)C changes but are instead local phenomena.}, language = {en} } @article{KienelPlessenSchettleretal.2013, author = {Kienel, Ulrike and Plessen, Birgit and Schettler, Georg and Weise, Stephan and Pinkerneil, Sylvia and Boehnel, Harald and Englebrecht, Amy C. and Haug, Gerald H.}, title = {Sensitivity of a hypersaline crater lake to the seasonality of rainfall, evaporation, and guano supply}, series = {Fundamental and applied limnology : official journal of the International Association of Theoretical and Applied Limnology}, volume = {183}, journal = {Fundamental and applied limnology : official journal of the International Association of Theoretical and Applied Limnology}, number = {2}, publisher = {Schweizerbart}, address = {Stuttgart}, issn = {1863-9135}, doi = {10.1127/1863-9135/2013/0405}, pages = {135 -- 152}, year = {2013}, abstract = {The hypersaline crater lake and its catchment on seabird island Isabel (Pacific, off Mexico) was studied to explore the influence of strong seasonal variations in rainfall/evaporation and guano contribution on its limnology. The hypersaline lake water (HSW, 78 \%) is up to 2.2-times enriched in inert ions relative to mean seawater. Rainfall during summer dilutes the HSW to form a less saline rainwater body (RWB) above a chemolimnion between 2 and 4 m water depth. The RWB is inhabited first by diatoms and ostracods followed later on by cyanobacteria and ciliates. Evaporation of > 1.5 m depth of lake water over the dry season increases the salinity of the RWB until the water column becomes isohaline at HSW concentrations in the late dry season. Differences in the stable isotope composition of water and primary producers in RWB and HSW reflect this development. Introduction of seabird guano and the decrease of salinity fuel a high primary production in the RWB with higher delta(CDIC)-C-13 and delta(13)Corg of particulate organic matter than in the HSW. The high N supply leads to high delta N-15 NH4 values (+ 39 \% in the HSW) as the consequence of ammonia volatilization that is strongest during guano maturation and with evaporative salinity increase from the HSW. Precipitation of carbonate (calcite and aragonite) from the RWB and the HSW is hindered by the high concentration of guano-derived P. This inhibition may be overcome with evaporative supersaturation during particularly dry conditions. Carbonate may also precipitate during particularly wet conditions from the dilute RWB, where the P-concentration is reduced during an active phytoplankton production that raises the pH. Differences in the stable isotope signatures of carbon and oxygen in HSW and RWB (+ 5 \% delta(CDIC)-C-13 and -3 \% d18OH2O) suggest the processes of carbonate precipitation can be distinguished based on the isotope signature of the carbonates deposited. Changes in the lake system are indicated when lower temperatures and higher rainfall in the 2006 wet season introduced more and less mature guano to the lake. The lower pH was accompanied by lower ammonia volatilization and carbonate precipitation as indicated by an increased concentration of NH4, Ca, Sr and DIC, while delta H-2, delta(NNH4)-N-15, and salinity were lower. According to our results, the observed sediment laminations should reflect the introduction of catchment material (including guano) with runoff, the RWB plankton production, and the carbonate precipitation in relation to its origin and seasonality.}, language = {en} } @article{NaafsHefterFerrettietal.2011, author = {Naafs, B. David A. and Hefter, Jens and Ferretti, Patrizia and Stein, R{\"u}diger and Haug, Gerald H.}, title = {Sea surface temperatures did not control the first occurrence of Hudson Strait Heinrich Events during MIS 16}, series = {Paleoceanography}, volume = {26}, journal = {Paleoceanography}, number = {4}, publisher = {American Geophysical Union}, address = {Washington}, issn = {0883-8305}, doi = {10.1029/2011PA002135}, pages = {10}, year = {2011}, abstract = {Hudson Strait (HS) Heinrich Events, ice-rafting events in the North Atlantic originating from the Laurentide ice sheet (LIS), are among the most dramatic examples of millennial-scale climate variability and have a large influence on global climate. However, it is debated as to whether the occurrence of HS Heinrich Events in the (eastern) North Atlantic in the geological record depends on greater ice discharge, or simply from the longer survival of icebergs in cold waters. Using sediments from Integrated Ocean Drilling Program (IODP) Site U1313 in the North Atlantic spanning the period between 960 and 320 ka, we show that sea surface temperatures (SSTs) did not control the first occurrence of HS Heinrich(-like) Events in the sedimentary record. Using mineralogy and organic geochemistry to determine the characteristics of ice-rafting debris (IRD), we detect the first HS Heinrich(-like) Event in our record around 643 ka (Marine Isotope Stage (MIS) 16), which is similar as previously reported for Site U1308. However, the accompanying high-resolution alkenone-based SST record demonstrates that the first HS Heinrich(-like) Event did not coincide with low SSTs. Thus, the HS Heinrich(-like) Events do indicate enhanced ice discharge from the LIS at the end of the Mid-Pleistocene Transition, not simply the survivability of icebergs due to cold conditions in the North Atlantic.}, language = {en} } @article{WolffHaugTimmermannetal.2011, author = {Wolff, Christian Michael and Haug, Gerald H. and Timmermann, Axel and Damste, Jaap S. Sinninghe and Brauer, Achim and Sigman, Daniel M. and Cane, Mark A. and Verschuren, Dirk}, title = {Reduced interannual rainfall variability in East Africa during the last Ice Age}, series = {Science}, volume = {333}, journal = {Science}, number = {6043}, publisher = {American Assoc. for the Advancement of Science}, address = {Washington}, issn = {0036-8075}, doi = {10.1126/science.1203724}, pages = {743 -- 747}, year = {2011}, abstract = {Interannual rainfall variations in equatorial East Africa are tightly linked to the El Nino Southern Oscillation (ENSO), with more rain and flooding during El Nino and droughts in La Nina years, both having severe impacts on human habitation and food security. Here we report evidence from an annually laminated lake sediment record from southeastern Kenya for interannual to centennial-scale changes in ENSO-related rainfall variability during the last three millennia and for reductions in both the mean rate and the variability of rainfall in East Africa during the Last Glacial period. Climate model simulations support forward extrapolation from these lake sediment data that future warming will intensify the interannual variability of East Africa's rainfall.}, language = {en} } @article{BakkeLieHeegaardetal.2009, author = {Bakke, Jostein and Lie, {\O}yvind and Heegaard, Einar and Dokken, Trond and Haug, Gerald H. and Birks, Hilary H. and Dulski, Peter and Nilsen, Trygve}, title = {Rapid oceanic and atmospheric changes during the Younger Dryas cold period}, issn = {1752-0894}, doi = {10.1038/ngeo439}, year = {2009}, abstract = {The Younger Dryas event, which began approximately 12,900 years ago, was a period of rapid cooling in the Northern Hemisphere, driven by large-scale reorganizations of patterns of atmospheric and oceanic circulation(1-3). Environmental changes during this period have been documented by both proxy-based reconstructions(3) and model simulations(4), but there is currently no consensus on the exact mechanisms of onset, stabilization or termination of the Younger Dryas(5-8). Here we present high-resolution records from two sediment cores obtained from Lake Krakenes in western Norway and the Nordic seas. Multiple proxies from Lake Krakenes are indicative of rapid alternations between glacial growth and melting during the later Younger Dryas. Meanwhile, reconstructed sea surface temperature and salinity from the Nordic seas show an alternation between sea-ice cover and the influx of warm, salty North Atlantic waters. We suggest that the influx of warm water enabled the westerly wind systems to drift northward, closer to their present-day positions. The winds thus brought relatively warm maritime air to Northern Europe, resulting in rising temperatures and the melting of glaciers. Subsequent input of this fresh meltwater into the ocean spurred the formation of sea ice, which forced the westerly winds back to the south, cooling Northern Europe. We conclude that rapid alternations between these two states immediately preceded the termination of the Younger Dryas and the permanent transition to an interglacial state.}, language = {en} } @article{HaugSigman2009, author = {Haug, Gerald H. and Sigman, Daniel M.}, title = {Palaeoceanography : polar twins}, issn = {1752-0894}, doi = {10.1038/Ngeo423}, year = {2009}, abstract = {Ice ages in the North Pacific Ocean and the Southern Ocean were marked by low productivity. Accumulating evidence indicates that strong stratification restricted the supply of nutrients from the deep ocean to the algae of the sunlit surface in these regions.}, language = {en} } @article{KwiecienArzLamyetal.2009, author = {Kwiecien, Olga and Arz, Helge Wolfgang and Lamy, Frank and Plessen, Birgit and Bahr, Andr{\´e} and Haug, Gerald H.}, title = {North Atlantic control on precipitation pattern in the eastern Mediterranean/Black Sea region during the last glacial}, issn = {0033-5894}, doi = {10.1016/j.yqres.2008.12.004}, year = {2009}, abstract = {Based on Proxy records from western Black Sea cores, we provide a comprehensive Study of climate change during the last glacial maximum and late-glacial period in the Black Sea region. For the first time we present a record of relative changes in precipitation for NW Anatolia based on variations in the terrigenous supply expressed as detrital carbonate concentration. The good correspondence between reconstructed rainfall intensity in NW Anatolia and past western Mediterranean sea Surface temperatures (SSTs) implies that during the glacial period the precipitation variability was controlled, like today, by Mediterranean cyclonic disturbances. Periods of reduced precipitation correlate well with low SSTs in the Mediterranean related to Heinrich events H1 and H2. Stable oxygen isotopes and lithological and mineralogical data point to a significant modification in the dominant freshwater/sediment source concomitant to the meltwater inflow after 16.4 cal ka BP. This change implies intensification of the northern sediment source and, with other records from the Mediterranean region, consistently suggests a reorganization of the atmospheric circulation pattern affecting the hydrology of the European continent. The early deglacial northward retreat of both atmospheric and oceanic polar fronts was responsible for the warming in the Mediterranean region, leading simultaneously to more humid conditions in central and northern Europe.}, language = {en} } @article{WolffKristenJennySchettleretal.2014, author = {Wolff, Christian Michael and Kristen-Jenny, Iris and Schettler, Georg and Plessen, Birgit and Meyer, Hanno and Dulski, Peter and Naumann, Rudolf and Brauer, Achim and Verschuren, Dirk and Haug, Gerald H.}, title = {Modern seasonality in Lake Challa (Kenya/Tanzania) and its sedimentary documentation in recent lake sediments}, series = {Limnology and oceanography}, volume = {59}, journal = {Limnology and oceanography}, number = {5}, publisher = {Wiley}, address = {Waco}, issn = {0024-3590}, doi = {10.4319/lo.2014.59.5.1621}, pages = {1621 -- 1636}, year = {2014}, abstract = {From November 2006 to January 2010, a sediment trap that was cleared monthly was deployed in Lake Challa, a deep stratified freshwater lake on the eastern slope of Mt. Kilimanjaro in southern Kenya. Geochemical data from sediment trap samples were compared with a broad range of limnological and meteorological parameters to characterize the effect of single parameters on productivity and sedimentation processes in the crater basin. During the southern hemisphere summer (November-March), when the water temperature is high and the lake is biologically productive (nondiatom algae), calcite predominated in the sediment trap samples. During the "long rain" season (March-May) a small amount of organic matter and lithogenic material caused by rainfall appeared. This was followed by the cool and windy months of the southern hemisphere winter (June-October) when diatoms were the main component, indicating a diatom bloom initiated by improvement of nutrient availability related to upwelling processes. The sediment trap data support the hypothesis that the light-dark lamination couplets, which are abundant in Lake Challa cores, reflect seasonal delivery to the sediments of diatom-rich particulates during the windy months and diatom-poor material during the wet season. However, interannual and spatial variability in upwelling and productivity patterns, as well as El Nino-Southern Oscillation (ENSO)-related rainfall and drought cycles, exert a strong influence on the magnitude and geochemical composition of particle export to the hypolimnion of Lake Challa.}, language = {en} } @article{DeplazesLueckgePetersonetal.2013, author = {Deplazes, Gaudenz and Lueckge, Andreas and Peterson, Larry C. and Timmermann, Axel and Hamann, Yvonne and Hughen, Konrad A. and Roehl, Ursula and Laj, Carlo and Cane, Mark A. and Sigman, Daniel M. and Haug, Gerald H.}, title = {Links between tropical rainfall and North Atlantic climate during the last glacial period}, series = {Nature geoscience}, volume = {6}, journal = {Nature geoscience}, number = {3}, publisher = {Nature Publ. Group}, address = {New York}, issn = {1752-0894}, doi = {10.1038/ngeo1712}, pages = {213 -- 217}, year = {2013}, abstract = {During the last glacial period, the North Atlantic region experienced pronounced, millennial-scale alternations between cold, stadial conditions and milder interstadial conditions-commonly referred to as Dansgaard-Oeschger oscillations-as well as periods of massive iceberg discharge known as Heinrich events(1). Changes in Northern Hemisphere temperature, as recorded in Greenland(2-4), are thought to have affected the location of the Atlantic intertropical convergence zone(5,6) and the strength of the Indian summer monsoon(7,8). Here we use high-resolution records of sediment colour-a measure of terrigenous versus biogenic content-from the Cariaco Basin off the coast of Venezuela and the Arabian Sea to assess teleconnections with the North Atlantic climate system during the last glacial period. The Cariaco record indicates that the intertropical convergence zone migrated seasonally over the site during mild stadial conditions, but was permanently displaced south of the basin during peak stadials and Heinrich events. In the Arabian Sea, we find evidence of a weak Indian summer monsoon during the stadial events. The tropical records show a more variable response to North Atlantic cooling than the Greenland temperature records. We therefore suggest that Greenland climate is especially sensitive to variations in the North Atlantic system-in particular sea-ice extent-whereas the intertropical convergence zone and Indian monsoon system respond primarily to variations in mean Northern Hemisphere temperature.}, language = {en} } @article{VerschurenDamsteMoernautetal.2009, author = {Verschuren, Dirk and Damst{\´e}, Jaap S. Sinninghe and Moernaut, Jasper and Kristen, Iris and Blaauw, Maarten and Fagot, Maureen and Haug, Gerald H.}, title = {Half-precessional dynamics of monsoon rainfall near the East African Equator}, issn = {0028-0836}, doi = {10.1038/Nature08520}, year = {2009}, abstract = {External climate forcings-such as long-term changes in solar insolation-generate different climate responses in tropical and high latitude regions(1). Documenting the spatial and temporal variability of past climates is therefore critical for understanding how such forcings are translated into regional climate variability. In contrast to the data- richmiddle and high latitudes, high-quality climate-proxy records from equatorial regions are relatively few(2-4), especially from regions experiencing the bimodal seasonal rainfall distribution associated with twice-annual passage of the Intertropical Convergence Zone. Here we present a continuous and well-resolved climate-proxy record of hydrological variability during the past 25,000 years from equatorial East Africa. Our results, based on complementary evidence from seismic-reflection stratigraphy and organic biomarker molecules in the sediment record of Lake Challa near Mount Kilimanjaro, reveal that monsoon rainfall in this region varied at half-precessional (similar to 11,500-year) intervals in phase with orbitally controlled insolation forcing. The southeasterly and northeasterly monsoons that advect moisture from the western Indian Ocean were strengthened in alternation when the inter-hemispheric insolation gradient was at a maximum; dry conditions prevailed when neither monsoon was intensified and modest local March or September insolation weakened the rain season that followed. On sub-millennial timescales, the temporal pattern of hydrological change on the East African Equator bears clear high-northern-latitude signatures, but on the orbital timescale it mainly responded to low-latitude insolation forcing. Predominance of low-latitude climate processes in this monsoon region can be attributed to the low-latitude position of its continental regions of surface air flow convergence, and its relative isolation from the Atlantic Ocean, where prominent meridional overturning circulation more tightly couples low-latitude climate regimes to high-latitude boundary conditions.}, language = {en} } @article{BrunelleSigmanJaccardetal.2010, author = {Brunelle, Brigitte G. and Sigman, Daniel M. and Jaccard, Samuel Laurent and Keigwin, Lloyd D. and Plessen, Birgit and Schettler, Georg and Cook, Mea S. and Haug, Gerald H.}, title = {Glacial/interglacial changes in nutrient supply and stratification in the western subarctic North Pacific since the penultimate glacial maximum}, issn = {0277-3791}, doi = {10.1016/j.quascirev.2010.03.010}, year = {2010}, abstract = {In piston cores from the open subarctic Pacific and the Okhotsk Sea, diatom-bound delta N-15 (delta N-15(db)), biogenic opal, calcium carbonate, and barium were measured from coretop to the previous glacial maximum (MIS 6). Glacial intervals are generally characterized by high delta N-15(db) (similar to 8 parts per thousand) and low productivity, whereas interglacial intervals have a lower delta N-15(db) (5.7-6.3 parts per thousand) and indicate high biogenic productivity. These data extend the regional swath of evidence for nearly complete surface nutrient utilization during glacial maxima, consistent with stronger upper water column stratification throughout the subarctic region during colder intervals. An early deglacial decline in delta N-15(db) of 2 parts per thousand at similar to 17.5 ka, previously observed in the Bering Sea, is found here in the open subarctic Pacific record and arguably also in the Okhotsk, and a case can be made that a similar decrease in delta N-15(db) occurred in both regions at the previous deglaciation as well. The early deglacial delta N-15(db) decrease, best explained by a decrease in surface nutrient utilization, appears synchronous with southern hemisphere-associated deglacial changes and with the Heinrich 1 event in the North Atlantic. This delta N-15(db) decrease may signal the initial deglacial weakening in subarctic North Pacific stratification and/or a deglacial increase in shallow subsurface nitrate concentration. If the former, it would be the North Pacific analogue to the increase in vertical exchange inferred for the Southern Ocean at the time of Heinrich Event 1. In either case, the lack of any clear change in paleoproductivity proxies during this interval would seem to require an early deglacial decrease in the iron-to-nitrate ratio of subsurface nutrient supply or the predominance of light limitation of phytoplankton growth during the deglaciation prior to Bolling-Allerod warming.}, language = {en} } @article{RenStuderSernoetal.2015, author = {Ren, Haojia and Studer, Anja S. and Serno, Sascha and Sigman, Daniel M. and Winckler, Gisela and Anderson, Robert F. and Oleynik, Sergey and Gersonde, Rainer and Haug, Gerald H.}, title = {Glacial-to-interglacial changes in nitrate supply and consumption in the subarctic North Pacific from microfossil-bound N isotopes at two trophic levels}, series = {Paleoceanography}, volume = {30}, journal = {Paleoceanography}, number = {9}, publisher = {American Geophysical Union}, address = {Washington}, issn = {0883-8305}, doi = {10.1002/2014PA002765}, pages = {1217 -- 1232}, year = {2015}, abstract = {Reduced nitrate supply to the subarctic North Pacific (SNP) surface during the last ice age has been inferred from coupled changes in diatom-bound delta N-15 (DB-delta N-15), bulk sedimentary delta N-15, and biogenic fluxes. However, the reliability of bulk sedimentary and DB-delta N-15 has been questioned, and a previously reported delta N-15 minimum during Heinrich Stadial 1 (HS1) has proven difficult to explain. In a core from the western SNP, we report the foraminifera-bound delta N-15 (FB-delta N-15) in Neogloboquadrina pachyderma and Globigerina bulloides, comparing them with DB-delta N-15 in the same core over the past 25 kyr. The delta N-15 of all recorders is higher during the Last Glacial Maximum (LGM) than in the Holocene, indicating more complete nitrate consumption. N. pachyderma FB-delta N-15 is similar to DB-delta N-15 in the Holocene but 2.2\% higher during the LGM. This difference suggests a greater sensitivity of FB-delta(15)NZ to changes in summertime nitrate drawdown and delta N-15 rise, consistent with a lag of the foraminifera relative to diatoms in reaching their summertime production peak in this highly seasonal environment. Unlike DB-delta N-15, FB-delta N-15 does not decrease from the LGM into HS1, which supports a previous suggestion that the HS1 DB-delta N-15 minimum is due to contamination by sponge spicules. FB-delta N-15 drops in the latter half of the Bolling/Allerod warm period and rises briefly in the Younger Dryas cold period, followed by a decline into the mid-Holocene. The FB-delta N-15 records suggest that the coupling among cold climate, reduced nitrate supply, and more complete nitrate consumption that characterized the LGM also applied to the deglacial cold events.}, language = {en} }