Sea surface temperature reconstruction from biomarker in sediments off Portugal

High resolution reconstructions of sea surface temperature (Uk'37-SST), coccolithophore associations and continental input (total organic carbon, higher plant n-alkanes, n-alkan-1-ols) in core D13882 from the shallow Tagus mud patch are compared to SST records from deep-sea core MD03-2699 and other western Iberian Margin cores. Results reveal millennial-scale climate variability over the last deglaciation, in particular during the LGIT. In the Iberian margin, Heinrich event 1 (H1) and the Younger Dryas (YD) represent two extreme episodes of cold sea surface condition separated by a marine warm phase that coincides with the Bølling-Allerød interval (B-A) on the neighboring continent. Following the YD event, an abrupt sea surface warming marks the beginning of the Holocene in this region. SSTs recorded in core D13882 changed, however, faster than those at deep-sea site MD03-2699 and at the other available palaeoclimate sequences from the region. While the SST values from most deep-sea cores reflect the latitudinal gradient detected in the Iberian Peninsula atmospheric temperature proxies during H1 and the B-A, the Tagus mud patch (core D13882) experienced colder SSTs during both events. This is most certainly related to a supplementary input of cold freshwater from the continent to the Tagus mud patch, a hypothesis supported by the high contents of terrigenous biomarkers and total organic carbon as well as by the dominance of tetra-unsaturated alkenone (C37:4) observed at this site. The comparison of all western Iberia SST records suggests that the SST increase that characterizes the B-A event in this region started 1000 yr before meltwater pulse 1A (mwp-1A) and reached its maximum values during or slightly after this episode of substantial sea-level rise. In contrast, during the YD/ Holocene transition, the sharp SST rise in the Tagus mud patch is synchronous with meltwater pulse IB. The decrease of continental input to the mud patch conflrms a sea level rise in the region. Thus, the synchronism between the maximum warming in the mid-latitudes off the western Iberian margin, the adjacent landmasses and Greenland indicates that mwp-lB and the associated sea-level rise probably initiated in the Northern Hemisphere rather than in the South.

Radiocarbon ages and average physical properties of sediment cores obtained during Icebreaker Oden cruise OSO0910

To date, understanding of ice sheet retreat within Pine Island Bay (PIB) following the Last Glacial Maximum (LGM) was based on seven radiocarbon dates and only fragmentary seafloor geomorphic evidence. During the austral summer 2009-2010, restricted sea ice cover allowed for the collection of 27 sediment cores from the outer PIB trough region. Combining these cores with data from prior cruises, over 133 cores have been used to conduct a detailed sedimentological facies analysis. These results, augmented by 23 new radiocarbon dates, are used to reconstruct the post-LGM deglacial history of PIB. Our results record a clear retreat stratigraphy in PIB composed of, from top to base; terrigenous sandy silt (distal glacimarine), pebbly sandy mud (ice-proximal glacimarine), and till. Initial retreat from the outer-continental shelf began shortly after the LGM and before 16.4 k cal yr BP, as a likely response to rising sea level. Bedforms in outer PIB document episodic retreat in the form of back-stepping grounding zone wedges and are associated with proximal glacimarine sediments. A sub-ice shelf facies is observed in central PIB and spans ~12.3-10.6 k cal yr BP. It is possible that widespread impingement of warm water onto the continental shelf caused an abrupt and widespread change from sub-ice shelf sedimentation to distal glacimarine sedimentation dominated by widespread dispersal of terrigenous silt between 7.8 and 7.0 k cal yr BP. The final phase of retreat ended before ~1.3 k cal yr BP, when the grounding line migrated to a location near the current ice margin.

Sedimentology on sediment cores from the eastern Weddell Sea, Antarctica

Sediment cores from nine sites along a profile on the Antarctic continental margin off Kapp Norvegia were analysed sedimentologicaly. The carbonate and organic carbon content, grain size distribution, composition of the coarse fraction and clay minerals were determined. d18O- and d13C-isotope ratios were also measured. The distribution of ice rafted debris was determined by a new method. Sedimentation-rates were obtained from 230Th- and 14C-analyses. A segregation into seven different sediment facies was made possible by different sedimentological parameters, which can be attributed to different sedimentation environments and conditions. Thr profile can be divided morphologicaly into shelf, upper continental slope, slope terrace and lower continental slope. The paratill facies is deposited on the shelf during an interglacial phase and consists mainly of ice rafted sediments. A portion of the fine fraction is being carried away by the antarctic coastel current. The sedimentation rate lies between 0 and 3 cm/1000 a. The coarse grained deposits of the upper, relatively steep continental slope, were specified as a rest sediment. Current and gravity sediment transport are responsible for the intensive sorting of ice rafted material coming from the shelf. The fine sediment is carried away by currents while sand and silt are deposited as small turbidites on the slope terrace. The morainic facies only appears at the base of the upper continental slope and defines ice advances, beyond the shelf margin. The facies mainly consists of transported shelf sediments. The interglacial facies, deposited during the interglacial phases on the continental slope, are characterized by high proportions of ice raft, coarse mean grain size, low content of montmorillonite and a carbonate content, which mainly originates from planktonic foraminifera (N. pachyderma). At the central part of the slope the sedimentation rate is at its lowest (2 cm/1000 a) and increases to 3-4 cm/1000 a towards the sea, due to high production of biogenic components and towards the continent due to an increasing input of terrigenous material. Sedimentary conditions during glacial times are depicted in the glacial facies by a low content of ice rafted debris, a lower mean grain size and a high content of montmorillonite. Biogeneous components are absent. The sedimentation rate is generally about 1 cm/1000a. A transition facies is deposited during the transition from glacial to interglacial conditions. Typical for this facies, with a terrigenous composition similar to the interglacial facies, is a high content of radiolaria. The reason for the change of plankton from a siliceous to a carbonacous fauna may have been the changing hydrography caused by the sea ice. The surge facies is deposited at the continental margin under the ice shelf and is a sediment exclusively delivered by currents. With the aid of this facies it was, for the first time possible to prove the existence of Antarctic ice surges, an aspect wh ich has been discussed for the past 20 years.

Sedimentology, biogeochemistry stable isotopes, pollen, plant macrofossils, and diatoms from two sediments cores from the northern Yukon permafrost peatlands (Canada)

Ice-wedge polygon (IWP) mires in the Arctic and Subarctic are extremely vulnerable to climatic and environmental change. We present the results of a multidisciplinary paleoenvironmental study on IWPs in the northern Yukon, Canada. High-resolution laboratory analyses were carried out on a permafrost core and the overlying seasonally thawed (active) layer, from a low-centered IWP located in a drained lake basin on Herschel Island. In relation to 14 Accelerator Mass Spectrometry (AMS) radiocarbon dates spanning the last 5000 years, we report sedimentary data including grain size distribution and biogeochemical parameters (organic carbon, nitrogen, C/N ratio, d13C), stable water isotopes (d18O, dD), as well as fossil pollen, plant macrofossil and diatom assemblages. Three sediment units (SUs) correspond to the main stages of deposition (1) in a thermokarst lake (SU1: 4950 to 3950 cal yrs BP), (2) during transition from lacustrine to palustrine conditions after lake drainage (SU2: 3950 to 3120 cal yrs BP), and (3) in palustrine conditions in the IWP field that developed after drainage (SU3: 3120 cal yrs BP to AD 2012). The lacustrine phase (pre 3950 cal yrs BP) is characterized by planktonic-benthic and pioneer diatoms species indicating circumneutral waters, and very few plant macrofossils. The pollen record has captured a regional signal of relatively stable vegetation composition and climate for the lacustrine stage of the record until 3950 cal yrs BP. Palustrine conditions with benthic and acidophilic species characterize the peaty shallow-water environments of the low-centered IWP. The transition from lacustrine to palustrine conditions was accompanied by acidification and rapid revegetation of the lake bottom within about 100 years. Since the palustrine phase we consider the pollen record as a local vegetation proxy dominated by the plant communities growing in the IWP. Ice-wedge cracking in water-saturated sediments started immediately after lake drainage at about 3950 cal yrs BP and led to the formation of an IWP mire. Permafrost aggradation through downward closed-system freezing of the lake talik is indicated by the stable water isotope record. The originally submerged IWP center underwent gradual drying during the past 2000 years. This study highlights the sensitivity of permafrost landscapes to climate and environmental change throughout the Holocene.

Palynological and geochemical data of sediment core GeoB3910-2 located offshore Northeast Brazil

High resolution palynological and geochemical data of sediment core GeoB 3910-2 (located offshore Northeast Brazil) spanning the period between 19 600 and 14 500 calibrated year bp (19.6-14.5 ka) show a land-cover change in the catchment area of local rivers in two steps related to changes in precipitation associated with Heinrich Event 1 (H1 stadial). At the end of the last glacial maximum, the landscape in semi-arid Northeast Brazil was dominated by a very dry type of caatinga vegetation, mainly composed of grasslands with some herbs and shrubs. After 18 ka, considerably more humid conditions are suggested by changes in the vegetation and by Corg and C/N data indicative of fluvial erosion. The caatinga became wetter and along lakes and rivers, sedges and gallery forest expanded. The most humid period was recorded between 16.5 and 15 ka, when humid gallery (and floodplain) forest and even small patches of mountainous Atlantic rain forest occurred together with dry forest, the latter being considered as a rather lush type of caatinga vegetation. During this humid phase erosion decreased as less lithogenic material and more organic terrestrial material were deposited on the continental slope of northern Brazil. After 15 ka arid conditions returned. During the humid second phase of the H1 stadial, a rich variety of landscapes existed in Northeast Brazil and during the drier periods small pockets of forest could probably survive in favorable spots, which would have increased the resilience of the forest to climate change.

Geochemical and rock magnetic investigation of sediment cores of the western South Atlantic

Geochemical and rock magnetic investigations of sediments from three sites on the continental margin off Argentina and Uruguay were carried out to study diagenetic alteration of iron minerals driven by anaerobic oxidation of methane (AOM). The western Argentine Basin represents a suitable sedimentary environment to study nonsteady-state processes because it is characterized by highly dynamic depositional conditions. Mineralogic and bulk solid phase data document that the sediment mainly consists of terrigenous material with high contents of iron minerals. As a typical feature of these deposits, distinct minima in magnetic susceptibility (k) are observed. Pore water data reveal that these minima in susceptibility coincide with the current depth of the sulfate/methane transition (SMT) where HS- is generated by the process of AOM. The released HS- reacts with the abundant iron (oxyhydr)oxides resulting in the precipitation of iron sulfides accompanied by a nearly complete loss of magnetic susceptibility. Modeling of geochemical data suggest that the magnetic record in this area is highly influenced by a drastic change in mean sedimentation rate (SR) which occurred during the Pleistocene/Holocene transition. We assume that the strong decrease in mean SR encountered during this glacial/interglacial transition induced a fixation of the SMT at a specific depth. The stagnation has obviously enhanced diagenetic dissolution of iron (oxyhydr)oxides within a distinct sediment interval. This assumption was further substantiated by numerical modeling in which the mean SR was decreased from 100 cm/kyr during glacial times to 5 cm/kyr in the Holocene and the methane flux from below was fixed to a constant value. To obtain the observed geochemical and magnetic patterns, the SMT must remain at a fixed position for ~9000 yrs. This calculated value closely correlates to the timing of the Pleistocene/Holocene transition. The results of the model show additionally that a constant high mean SR would cause a concave-up profile of pore water sulfate under steady state conditions.

Climate sensitivity across marine domains of life: limits to evolutionary adaptation shape species interactions, supplementary material

Organisms in all domains, Archaea, Bacteria, and Eukarya will respond to climate change with differential vulnerabilities resulting in shifts in species distribution, coexistence, and interactions. The identification of unifying principles of organism functioning across all domains would facilitate a cause and effect understanding of such changes and their implications for ecosystem shifts. For example, the functional specialization of all organisms in limited temperature ranges leads us to ask for unifying functional reasons. Organisms also specialize in either anoxic or various oxygen ranges, with animals and plants depending on high oxygen levels. Here, we identify thermal ranges, heat limits of growth, and critically low (hypoxic) oxygen concentrations as proxies of tolerance in a meta-analysis of data available for marine organisms, with special reference to domain-specific limits. For an explanation of the patterns and differences observed, we define and quantify a proxy for organismic complexity across species from all domains. Rising complexity causes heat (and hypoxia) tolerances to decrease from Archaea to Bacteria to uni- and then multicellular Eukarya. Within and across domains, taxon-specific tolerance limits likely reflect ultimate evolutionary limits of its species to acclimatization and adaptation. We hypothesize that rising taxon-specific complexities in structure and function constrain organisms to narrower environmental ranges. Low complexity as in Archaea and some Bacteria provide life options in extreme environments. In the warmest oceans, temperature maxima reach and will surpass the permanent limits to the existence of multicellular animals, plants and unicellular phytoplankter. Smaller, less complex unicellular Eukarya, Bacteria, and Archaea will thus benefit and predominate even more in a future, warmer, and hypoxic ocean.

Pore water (SO4, CH4, alkalinity, HS-, Ca, Sr, Mg, Ba) and solid phase (Ca, Sr, Mg, Ba) data measured in pockmark sediments of the Northern Congo Fan

This study focuses on the vertical distribution of authigenic carbonates (aragonite and high Mg-calcite) in the form of finely disseminated precipitates as well as massive carbonate concretions present in and above gas hydrate bearing sediments of the Northern Congo Fan. Analyses of Ca, Mg, Sr and Ba in pore water, bulk sediments and authigenic carbonates were carried out on gravity cores taken from three pockmark structures (Hydrate Hole, Black Hole and Worm Hole). In addition, a background core was retrieved from an area not influenced by fluid seepage. Pore water Sr/Ca and Mg/Ca ratios are used to reveal the current depths of carbonate formation as well as the mineralogy of the authigenic precipitates. The Sr/Ca and Mg/Ca ratios of bulk sediments and massive carbonate concretions were applied to infer the presence and depth distribution of authigenic aragonite and high Mg-calcite, based on the approach presented by Bayon et al. [Bayon et al. (2007). Sr/Ca and Mg/Ca ratios in Niger Delta sediments: Implications for authigenic carbonate genesis in cold seep environments. Marine Geology 241(1-4), 93-109, doi:10.1016/j.margeo.2007.03.007]. We show that the approach developed by Bayon et al. (2007) for sediments of cold seeps of the Niger Delta is also suitable to identify the mineralogy of authigenic carbonates in pockmark sediments of the Congo Deep-Sea Fan. We expand this approach by combining interstitial with solid phase Sr/Ca and Mg/Ca ratios, which demonstrate that high Mg-calcite is the predominant authigenic carbonate that currently forms at the sulfate/methane reaction zone (SMRZ). This is the first study which investigates both solid phase and pore water signatures typical for either aragonite or high Mg-calcite precipitation for the same sediment cores and thus is able to identify active and fossil carbonate precipitation events. At all investigated pockmark sites fossil horizons of the SMRZ were deduced from high Mg-calcite located above and below the current depths of the SMRZ. Additionally, aragonite enrichments typical for high seepage rates were detected close to the sediment surface at these sites. However, active precipitation of aragonite as indicated by pore water characteristics only occurs at the Black Hole site. Dissolved and solid phase Ba concentrations were used to estimate the time the SMRZ was fixed at the current depths of the diagenetic barite fronts. The combined pore water and solid phase elemental ratios (Mg/Ca, Sr/Ca) and Ba concentrations allow the reconstruction of past changes in methane seepage at the investigated pockmark sites. At the Hydrate Hole and Worm Hole sites the time of high methane seepage was estimated to have ceased at least 600 yr BP. In contrast, a more recent change from a high flux to a more dormant stage must have occurred at the Black Hole site as evidenced by active aragonite precipitation at the sediment surface and a lack of diagenetic Ba enrichments.

Accumulation and composition of terrigenous material on Ceara rise over the past 55 Ma

Ceara Rise, located east the Amazon River mouth, is covered with a thick blanket of pelagic carbonate and hemipelagic terrigenous sediment. The terrigenous component has been extracted from 57 bulk sediment samples at Ocean Drilling Program (ODP) Sites 925 and 929 on Ceara Rise to obtain a Cenozoic record of riverine discharge from northern South America. From the early Eocene to early Miocene (55-20 Ma), terrigenous accumulation was dominated by moderate amounts of generally large-grained, gray to green sediment especially depleted in elements that are enriched in post-Archaean shale (e.g. Cs, Th, Yb). However, pulsed inputs of relatively small-grained, gray to green terrigenous sediment less depleted in the above elements occurred in the late Eocene and Oligocene. The accumulation of terrigenous sediment decreased significantly until 16.5 Ma. In the middle Miocene (16.5-13 Ma), terrigenous accumulation was dominated by small amounts of small-grained, tan sediment notably depleted in Na and heavy rare earth elements. The accumulation rate of terrigenous sediment increased markedly from the latest Miocene (10 Ma) to the present day, a change characterized by deposition of gray-green sediment enriched in elements that are enriched in post-Archaean shale. Observed changes in terrigenous sediment at Ceara Rise record tectonism and erosion in northern South America. The Brazil and Guyana shields supplied sediment to the eastern South American margin until the middle Miocene (20-16.5 Ma) when a period of thrusting, shortening and uplift changed the source region, probably first to highly weathered and proximal Phanerozoic sediments. By the late Miocene (9 Ma), there was a transcontinental connection between the Andes and eastern South America. Weathering products derived from the Andes have increasingly dominated terrigenous deposition at Ceara Rise since the Late Miocene and especially since the late Pliocene.