Late Quaternary variability of sea-ice cover, surfac ewater temperature and terrigenous input in the subarctic North Pacific and the Bering Sea: A biomarker approach.

Over the last three decades, the Bering Sea has undergone dramatic changes in its physical and biological environment due to anthropogenic warming, accompanied by a dramatic shift in sea-ice cover, thickness, and duration of the ice season. These recent observations have increased the interest of the paleo-community in reconstructing the past variability of sea-surface characteristics in this region. The main objectives of this study were the millennial-scale reconstruction of the variability of surface-water conditions and terrigenous input in the subarctic Pacific and Bering Sea over the last glacial-deglacial-Holocene time interval (25 ka) in order to investigate their relationship to global climate change. For this purpose, changes in organic geochemical composition in surface sediments and sediment cores, collected during the SO202- INOPEX RV Sonne and SO201-KALMAR R/V Sonne cruises were investigated. The main results of this thesis are presented in three manuscripts. In order to determine the applicability of specific biomarkers, in view of future paleoclimatologic and paleoceanographic reconstructions in the subarctic Pacific and the Bering Sea, the first manuscript was dedicated to the reconstruction of modern sea-surface characteristics, i.e., sea-surface temperature (SST) and sea-ice cover in this area. Based on hydrogen index values and the distribution of long-chain n-alkanes and specific sterols in surface sediment, we show that different organic carbon sources prevailed in the study area. In the Bering Sea, organic matter has a predominantly marine origin, caused by high primary production, whereas in the North Pacific, organic carbon originates mostly from terrestrial higher plants, probably related to dust input from Asia. The results from the alkenone-based SST reconstruction demonstrate that the Sikes et al. (1997) calibration seems to be more accurate and matches the summer SSTs in the eastern North Pacific and the Bering Sea better than the Müller et al. (1998) calibration. In this study, we also show that the distribution of the novel sea-ice proxy IP25 in surface sediments mirror the modern spring sea-ice distribution and demonstrates the potential of this proxy to track past variations in sea-ice cover in the study area.In the second manuscript we use IP25 abundances,alkenone-based sea-surface temperatures, diatom and biogenic opal data from three sediment cores from the western North Pacific and western Bering Sea to reconstruct the variability of sea-ice extent during the past 18 ka. In general, there is a very good correlation between the biomarkers-based and the diatoms-based sea-ice records. The results demonstrate that a dominantly permanent sea-ice cover prevailed in the western Bering Sea during cold periods (Heinrich Stadial 1 and Younger Dryas), whereas reduced sea-ice or ice-free conditions existed during warmer intervals (Bølling/Allerød and Holocene). Warm intervals of reduced sea ice coincide with increased biogenic opal, indicating increased primary production. In the last manuscript, the millennial-scale of sea-ice reconstruction was extended to include the northeastern Bering Sea and the eastern and western subarctic Pacific. The results show that an extensive sea-ice cover prevailed over large parts of the subarctic Pacific and the Bering Sea during the LGM. The deglaciation-Holocene time interval is characterized by rapid sea-ice advance and retreat. During cold periods (Heinrich Stadial 1 and Younger Dryas) seasonal sea-ice cover generally coincides with low alkenone SSTs and low primary productivity. Conversely, during warmer intervals (Bølling/Allerød and Holocene) predominance of reduced sea ice or ice-free conditions are generally associated with increase in alkenone SSTs and primary productivity. However, in the northern Bering Sea continental shelf ice-free conditions prevailing during the Holocene Thermal Maximum shifted to marginal sea-ice conditions at the onset of the Mid Holocene. In summary, the work in this thesis demonstrates that sea-ice extent in the subarctic Pacific and the Bering Sea was highly variable during the last 25,000 years. The variability can be explained by a combination of local factors (e.g. solar insolation), as well as global climate anomalies (e.g. Bølling/Allerød and Younger Dryas) and sea-level changes controlling the oceanographic circulation between the subarctic Pacific and the Bering Sea

Modern spatial sea-ice variability in the central Arctic Ocean and adjacent marginal seas: Reconstruction from biomarker data

Sea ice is a fundamental component of Earth’s climate system, contributing to heat reduction (albedo) and deep-water formation. In order to understand processes controlling the recent dramatic reduction in Arctic sea-ice cover, it is essential to determine spatial and temporal changes in sea-ice occurrence and its natural variability in the present and past. Here, we present biomarker data from surface sediments and related to the modern spatial (seasonal) sea-ice variability in the central Arctic Ocean and adjacent marginal seas (i.e., Bering, Chukchi, Laptev and Kara seas) as well as the Fram Strait/Yermak Plateau area. We determined concentrations of the sea-ice diatom-derived biomarker “IP25″ (highly-branched isoprenoid – HBI – with 25 carbon atom; Belt et al., 2007), phytoplankton-derived biomarkers (brassicasterol and dinosterol) and terrigenous biomarkers (campesterol and Î_-sitosterol) to estimate recent sea-ice conditions in the study area. A combined phytoplankton-IP25 biomarker approach (“PIP25 index”; Müller et al., 2009, 2011) is used to reconstruct the modern sea-ice distribution more quantitatively. In addition, the distribution pattern of HBI-diene/IP25 ratios has been determined to test a proposed relationship between the diene/IP25 ratio and sea-surface temperatures in Arctic marginal ice-zone environments (Fahl and Stein, 2012; Stein et al., 2012). Assessment of sea-ice conditions based on these biomarker data display that a quite stable marginal ice zone exists along the continental shelf/slope of Kara and Laptev seas during summer/early fall. Elevated IP25 as well as brassicasterol and dinosterol values occurring in the central Kara and Laptev seas are related to extended sea-ice-cover and higher primary production (close to ice-edge situation). Further to the north and the central Arctic Ocean, lower IP25 and phytoplankton biomarker concentrations point to a more close sea-ice cover situation

Prebiotic effects: metabolic and health benefits

The different compartments of the gastrointestinal tract are inhabited by populations of micro-organisms. By far the most important predominant populations are in the colon where a true symbiosis with the host exists that is a key for well-being and health. For such a microbiota, 'normobiosis' characterises a composition of the gut 'ecosystem' in which micro-organisms with potential health benefits predominate in number over potentially harmful ones, in contrast to 'dysbiosis', in which one or a few potentially harmful micro-organisms are dominant, thus creating a disease-prone situation. The present document has been written by a group of both academic and industry experts (in the ILSI Europe Prebiotic Expert Group and Prebiotic Task Force, respectively). It does not aim to propose a new definition of a prebiotic nor to identify which food products are classified as prebiotic but rather to validate and expand the original idea of the prebiotic concept (that can be translated in 'prebiotic effects'), defined as: 'The selective stimulation of growth and/or activity(ies) of one or a limited number of microbial genus(era)/species in the gut microbiota that confer(s) health benefits to the host.' Thanks to the methodological and fundamental research of microbiologists, immense progress has very recently been made in our understanding of the gut microbiota. A large number of human intervention studies have been performed that have demonstrated that dietary consumption of certain food products can result in statistically significant changes in the composition of the gut microbiota in line with the prebiotic concept. Thus the prebiotic effect is now a well-established scientific fact. The more data are accumulating, the more it will be recognised that such changes in the microbiota's composition, especially increase in bifidobacteria, can be regarded as a marker of intestinal health. The review is divided in chapters that cover the major areas of nutrition research where a prebiotic effect has tentatively been investigated for potential health benefits. The prebiotic effect has been shown to associate with modulation of biomarkers and activity(ies) of the immune system. Confirming the studies in adults, it has been demonstrated that, in infant nutrition, the prebiotic effect includes a significant change of gut microbiota composition, especially an increase of faecal concentrations of bifidobacteria. This concomitantly improves stool quality (pH, SCFA, frequency and consistency), reduces the risk of gastroenteritis and infections, improves general well-being and reduces the incidence of allergic symptoms such as atopic eczema. Changes in the gut microbiota composition are classically considered as one of the many factors involved in the pathogenesis of either inflammatory bowel disease or irritable bowel syndrome. The use of particular food products with a prebiotic effect has thus been tested in clinical trials with the objective to improve the clinical activity and well-being of patients with such disorders. Promising beneficial effects have been demonstrated in some preliminary studies, including changes in gut microbiota composition (especially increase in bifidobacteria concentration). Often associated with toxic load and/or miscellaneous risk factors, colon cancer is another pathology for which a possible role of gut microbiota composition has been hypothesised. Numerous experimental studies have reported reduction in incidence of tumours and cancers after feeding specific food products with a prebiotic effect. Some of these studies (including one human trial) have also reported that, in such conditions, gut microbiota composition was modified (especially due to increased concentration of bifidobacteria). Dietary intake of particular food products with a prebiotic effect has been shown, especially in adolescents, but also tentatively in postmenopausal women, to increase Ca absorption as well as bone Ca accretion and bone mineral density. Recent data, both from experimental models and from human studies, support the beneficial effects of particular food products with prebiotic properties on energy homaeostasis, satiety regulation and body weight gain. Together, with data in obese animals and patients, these studies support the hypothesis that gut microbiota composition (especially the number of bifidobacteria) may contribute to modulate metabolic processes associated with syndrome X, especially obesity and diabetes type 2. It is plausible, even though not exclusive, that these effects are linked to the microbiota-induced changes and it is feasible to conclude that their mechanisms fit into the prebiotic effect. However, the role of such changes in these health benefits remains to be definitively proven. As a result of the research activity that followed the publication of the prebiotic concept 15 years ago, it has become clear that products that cause a selective modification in the gut microbiota's composition and/or activity(ies) and thus strengthens normobiosis could either induce beneficial physiological effects in the colon and also in extra-intestinal compartments or contribute towards reducing the risk of dysbiosis and associated intestinal and systemic pathologies

Deglacial-Holocene variability of sea ice and surface water temperature in the Bering Sea: Reconstruction based on “IP25“ and alkenone data

Overall goal of our study of sediment material collected during RV Sonne Cruise 202 (INOPEX) in 2009 (Gersonde et al., Curise Report 2009), is the reconstruction of the short-term variability of sea-ice, sea-surface temperature (SST), primary productivity and terrigenous input in the subpolar North Pacific/Bering Sea and their relationship to global climate change, using organic-geochemical proxies (i.e. organic-geochemical bulk parameters and biomarkers such as: TOC, hydrogen indices; long-chain n-alkanes, sterols, alkenones; Uk37 and TEX86-Index; BIT-Index; HBIs, IP25, PIP25). In a first phase, these organic-geochemical proxies have been determined in surface sediments. The results show that the biomarker proxies reflect modern sea-ice and SST distributions as well as areas of increased primary productivity and increased input of terrigenous (organic) matter quite well. In a second phase of the project, the biomarkers have been determined in three selected sediment cores: Core SO 202-18-6 (Umnak Plateau/Bering Sea; 60.127�N, 179.444�W; water depth 1105 m; core length 7.21 m; age interval 0 to 14 kyr.BP). Core SO 202-07-6 (Detroit Seamount/western subpolar North Pacific; 51.272�N, 167.700�W; water depth 2340 m WD; core length 4.69 m; age interval MIS 1 to 3). Core SO 202-27-6 (Patton Seamount/eastern subpolar North Pacific; 54.296�N, 149.600�W; water depth 2919 m; core length 2.91 m: age interval MIS 1 to 3). Here, we concentrate especially on the variability of sea-ice cover and SST, using the newly developed sea-ice proxy IP25 (Belt et al., 2007) and alkenone data, respectively, determined in the AMS14C-dated Core SO 202-18-6. Based on these biomarker records, sea-ice cover and SST changed significantly in the northern Bering Sea during Deglacial-Holocene times. The Younger Dryas interval is characterized by extended sea-ice cover, coinciding with a drop in SST to 2-4�C. With the end of the Younger Dryas, between 460 and 420 cmbsf, sea-ice cover decreased with increasing SST. Between 420 and 120 cmbsf representing the early Holocene (Thermal Maximum), IP25 is absent and maximum SST of about 6�C was reached. During the upper 120 cmbsf representing the late Holocene, IP25 occurred again and increased towards the top, paralleled by a decrease in SST of about 3�C. A very similar contemporaneous trend of increasing sea-ice cover during the late Holocene was recorded in the northernmost North Atlantic (Fram Strait), paralleled by an advance of glaciers in Norway, a colder climate over Greenland, a colder and dryer climate in Siberia, and a decrease in Siberian river discharge (Stein et al., 2004; Müller et al., 2009; 2012)

CHANGES OF SEA ICE AND SURFACE WATER TEMPERATURE IN THE BERING SEA DURING DEGLACIAL TO HOLOCENE TIMES: EVIDENCE FROM IP25 AND ALKENONE DATA

Overall goal of our study of sediment material collected during RV Sonne Cruise 202 (INOPEX) in 2009 (Gersonde et al., Curise Report 2009), is the reconstruction of the short-term variability of sea-ice, sea-surface temperature (SST), primary productivity and terrigenous input in the subpolar North Pacific/Bering Sea and their relationship to global climate change, using organic-geochemical proxies (i.e. organic-geochemical bulk parameters and specific biomarkers such as: TOC, hydrogen indices; long-chain n-alkanes, sterols, alkenones; Uk37 and TEX86-Index; BIT-Index; HBIs, IP25, PIP25). In a first phase, these organic-geochemical proxies have been determined in surface sediments. The results show that the biomarker proxies reflect modern sea-ice and SST distributions as well as areas of increased primary productivity and increased input of terrigenous (organic) matter quite well. In a second phase of the project, the biomarkers have been determined in three selected sediment cores: Core SO202-18-6 (Umnak Plateau/Bering Sea; 60.127°N, 179.444°W; water depth 1105 m; core length 7.21 m; age interval 0 to 14 kyr.BP). Core SO202-07-6 (Detroit Seamount/western subpolar North Pacific; 51.272°N, 167.700°W; water depth 2340 m WD; core length 4.69 m; age interval MIS 1 to 3). Core SO202-27-6 (Patton Seamount/eastern subpolar North Pacific; 54.296°N, 149.600°W; water depth 2919 m; core length 2.91 m: age interval MIS 1 to 3). Here, we concentrate especially on the variability of sea-ice cover and sea-surface temperature, using the newly developed sea-ice proxy IP25 (Belt et al., 2007) and alkenone data, respectively, determined in the AMS14C-dated Core SO202-18-6. Based on these biomarker records, sea-ice cover and SST changed significantly in the northern Bering Sea during Deglacial-Holocene times. The Younger Dryas interval is characterized by extended sea-ice cover, coinciding with a drop in SST to 2-4°C. With the end of the Younger Dryas, between 460 and 420 cmbsf, sea-ice cover decreased with increasing SST. Between 420 and 120 cmbsf representing the early Holocene Thermal Maximum, IP25 is absent and maximum SST of about 6°C was reached. During the upper 120 cmbsf representing the late Holocene, IP25 occurred again and increased towards the top, paralleled by a decrease in SST of about 3°C. A very similar contemporaneous trend of increasing sea-ice cover during the late Holocene was recorded in the northern North Atlantic, paralleled by an advance of glaciers in Norway (Müller et al., 2009; 2012)

Late Quaternary variability of sea-ice cover, surfac ewater @!temperature and terrigenous input in the subarctic @!North Pacific and the Bering Sea: A biomarker @!approach.

Over the last three decades, the Bering Sea has undergone dramatic changes in its physical and biological environment due to anthropogenic warming, accompanied by a dramatic shift in sea-ice cover, thickness, and duration of the ice season. These recent observations have increased the interest of the paleo-community in reconstructing the past variability of sea-surface characteristics in this region. @!The main objectives of this study were the millennial-scale reconstruction of the variability of surface-water conditions and terrigenous input in the subarctic Pacific and Bering Sea over the last glacial-deglacial-Holocene time interval (25 ka) in order to investigate their relationship to global climate change. For this purpose, @!changes in organic geochemical composition in surface sediments and sediment cores, collected during the SO202- INOPEX RV Sonne and SO201-KALMAR R/V Sonne cruises were investigated. The main results of this thesis are presented in three manuscripts. In order to determine the applicability of specific biomarkers, in view of future paleoclimatologic and paleoceanographic reconstructions in the subarctic Pacific and the Bering Sea, the first manuscript was dedicated to the reconstruction of modern sea-surface characteristics, i.e., sea-surface temperature (SST) and sea-ice cover in this area. Based on hydrogen index values and the distribution of long-chain n-alkanes and specific sterols in surface sediment, we show that different organic carbon sources prevailed in the study area. In the Bering Sea, organic matter has a predominantly marine origin, caused by high primary production, whereas in the North Pacific, organic carbon originates mostly from terrestrial higher plants, probably related to dust input from Asia. The results from the alkenone-based SST reconstruction demonstrate that the Sikes et al. (1997) calibration seems to be more accurate and matches the summer SSTs in the eastern North Pacific and the Bering Sea better than the Müller et al. (1998) calibration. In this study, we also show that the distribution of the novel sea-ice proxy IP25 in surface sediments mirror the modern spring sea-ice distribution and demonstrates the potential of this proxy to @!track past variations in sea-ice cover in the study area.In the second manuscript we use IP25 abundances,alkenone-based sea-surface temperatures, diatom and biogenic opal data from three sediment cores from the western North Pacific and western Bering Sea to reconstruct the variability of sea-ice extent during the past 18 ka. In general, there is a very good correlation between the biomarkers-based and the diatoms-based sea-ice records. The results demonstrate that a dominantly permanent sea-ice cover prevailed in the western Bering Sea during cold periods (Heinrich Stadial 1 and Younger Dryas), whereas reduced sea-ice or ice-free conditions existed during warmer intervals (Bølling/Allerød and Holocene). Warm intervals of reduced sea ice coincide with increased biogenic opal, indicating increased primary production. @!In the last manuscript, the millennial-scale of sea-ice reconstruction was extended to include the northeastern Bering Sea and the eastern and western subarctic Pacific. @!The results show that an extensive sea-ice cover prevailed over large parts of the subarctic Pacific and the Bering Sea during the LGM. The deglaciation-Holocene time interval is characterized by rapid sea-ice advance and retreat. During cold periods (Heinrich Stadial 1 and Younger Dryas) seasonal sea-ice cover generally coincides with low alkenone SSTs and low primary productivity. Conversely, during warmer intervals (Bølling/Allerød and Holocene) predominance of reduced sea ice or ice-free conditions are generally associated with increase in alkenone SSTs and @!primary productivity. However, in the northern Bering Sea continental shelf ice-free conditions prevailing during the Holocene Thermal Maximum shifted to marginal @!sea-ice conditions at the onset of the Mid Holocene. @!In summary, the work in this thesis demonstrates that sea-ice extent in the subarctic Pacific and the Bering Sea was highly variable during the last 25,000 years. @!The variability can be explained by a combination of local factors (e.g. solar insolation), as well as global climate anomalies (e.g. Bølling/Allerød and Younger Dryas) and sea-level changes controlling the oceanographic circulation between the subarctic Pacific and the Bering Sea

Sea-ice variability in the subarctic North Pacific and adjacent Bering Sea during the past 25 ka: new insights from IP25 and Uk′37 proxy records

This study focusses on the last glacial–deglacial–Holocene spatial and temporal variability in sea-ice cover based on organic geochemical analyses of marine sediment cores from the subarctic Pacific and the Bering Sea. By means of the sea-ice proxy “IP25” and phytoplankton-derived biomarkers (specific sterols and alkenones), we reconstruct the spring sea-ice conditions, (summer) sea-surface temperature (SST) and primary productivity, respectively. The large variability of sea ice was explained by a combination of local and global factors, such as solar insolation, global climate anomalies and sea-level changes controlling the oceanographic circulation and water mass exchange between the subarctic Pacific and the Bering Sea. During the Last Glacial Maximum, extensive sea-ice cover prevailed over large part of the subarctic Pacific and the Bering Sea. The following deglaciation is characterized by a rapid sea-ice advance and retreat. During cold periods (Heinrich Stadial 1 and Younger Dryas) seasonal sea-ice cover generally coincided with low alkenone SSTs and low primary productivity. Conversely, during warmer intervals (Bølling/Allerød, Early Holocene) reduced sea-ice or ice-free conditions prevailed in the study area. At the northern Bering Sea continental shelf a late-Early/Mid Holocene shift to marginal sea-ice conditions is in line with the simultaneous wide-spread sea-ice recovery observed in the other Arctic marginal seas and is likely initiated by the lower Northern Hemisphere insolation and surface-water cooling