Oxygen and carbon isotopic composition of shells from Radix sp. in lakes across the Tibetan Plateau

The Tibetan Plateau (TP), including its surrounding mountain ranges, represents the largest store of ice outside the polar regions. It hosts numerous lakes as well as the head waters of major Asian rivers, on which billions of people depend, and it is particularly sensitive to climate change. The moisture transport to the TP is controlled by the Indian and Pacific monsoon and the Westerlies. Understanding the evolution of the interaction of these circulation systems requires studies on climate archives in different spatial and temporal contexts. The objective of this study is to learn more about the interannual variability of precipitation patterns across the TP and how different hydrologic systems react to different climatic factors. Aragonite shells of the aquatic gastropod Radix, which is widely distributed in the region, may represent suitable archives for inferring hydrologic and climatic signals in particularly high resolution. Therefore, sclerochronological studies of d18O and d13C ratios in Radix shells from seven lakes were conducted, each representing a different hydrologic and climatic setting, on a transect from the Pamirs across the TP. The shell patterns exhibit an increasing influence of precipitation and a decreasing influence of evaporation on the isotope compositions from west to east. d18O values of shells from lakes on the eastern and central TP (Donggi Cona, Yamdrok Yumco, Tarab Co) mirror monsoon signals, indicated by more negative values and higher variabilities compared to the more western lakes (Karakul, Bangong/Nyak, Manasarovar). In Yadang Co, located on the central southern TP, the monsoon rains did not reach the lake in the sampling year, although it is located in a region which is usually affected by monsoon circulation. The d18O values are used to differentiate the annual hydrological cycle into ice cover period, melt water period, precipitation period and evaporation period. d13C compositions in the shells particularly depend on specific habitats, which vary in biological productivity and in carbon sources. d18O and d13C patterns show a positive covariance in shells originating from large closed basins. The results show that Radix shells mirror general climatic differences between the seven lake regions. These differences reflect both regional and local climate signals in sub-seasonal resolution, without noticeable dependence on the particular lake system.

Long chain 1,13- and 1,15-diols in surface sediments ans SST reconstruction for sediment core GeoB6518-1

Although commonly reported in marine and freshwater environments, little is known about the biological sources of long chain alkyl 1,13- and 1,15-diols, and factors controlling their distributions. Here we analyzed the occurrence and distribution of these lipids in a comprehensive set of marine surface sediments and compare their distributions with environmental conditions like sea surface temperature (SST), salinity and nutrient concentrations. Fractional abundances of the C28 1,13-, C30 1,13- and C30 1,15-diols show a strong correlation with SST and based on these results, we propose the Long chain Diol Index (LDI), which expresses the C30 1,15-diol abundance relative to those of C28 1,13-, C30 1,13- and C30 1,15-diols. The LDI shows a strong linear correlation with SST (LDI = 0.033 × SST + 0.095; R2 = 0.969, n = 162) over a temperature range of -3 to 27 °C. Long chain diol distributions in sediments from the South Atlantic close to the Congo River outflow (West Africa) provided a 43 kyr LDI SST record. This record reflects several known climatic events and shows similarities with an alkenone-derived SST record obtained using the same suite of sediments, both in trend and in terms of absolute SST. This confirms the potential of the LDI as a proxy for palaeo-SST reconstruction.

Average nutrient concentration, and growth characteristics of bacteria during USCGC Healy cruises in 2002 and 2004

Standing stocks and production rates for phytoplankton and heterotrophic bacteria were examined during four expeditions in the western Arctic Ocean (Chukchi Sea and Canada Basin) in the spring and summer of 2002 and 2004. Rates of primary production (PP) and bacterial production (BP) were higher in the summer than in spring and in shelf waters than in the basin. Most surprisingly, PP was 3-fold higher in 2004 than in 2002; ice-corrected rates were 1581 and 458 mg C/m**2/d respectively, for the entire region. The difference between years was mainly due to low ice coverage in the summer of 2004. The spatial and temporal variation in PP led to comparable variation in BP. Although temperature explained as much variability in BP as did PP or phytoplankton biomass, there was no relationship between temperature and bacterial growth rates above about 0°C. The average ratio of BP to PP was 0.06 and 0.79 when ice-corrected PP rates were greater than and less than 100 mg C/m**2/d, respectively; the overall average was 0.34. Bacteria accounted for a highly variable fraction of total respiration, from 3% to over 60% with a mean of 25%. Likewise, the fraction of PP consumed by bacterial respiration, when calculated from growth efficiency (average of 6.9%) and BP estimates, varied greatly over time and space (7% to >500%). The apparent uncoupling between respiration and PP has several implications for carbon export and storage in the western Arctic Ocean.

Physicochemical sea ice and water characteristics near Point Barrow 2005-2006

Photosynthetic parameters of phytoplankton and sea ice algae from landfast sea ice of the Chukchi Sea off Point Barrow, Alaska, were assessed in spring 2005 and winter through spring 2006 using Pulse Amplitude Modulated (PAM) fluorometry including estimates of maximum quantum efficiency (Fv/Fm), maximum relative electron transport rate (rETRmax), photosynthetic efficiency (alpha), and the photoadaptive index (Ek). The use of centrifuged brine samples allowed to document vertical gradients in ice algal acclimation with 5 cm vertical resolution for the first time. Bottom ice algae (0-5 cm from ice-water interface) expressed low Fv/Fm (0.331-0.426) and low alpha (0.098-0.130 /(µmol photons/m**2/s)) in December. Fv/Fm and alpha increased in March and May (0.468-0.588 and 0.141-0.438 /(µmol photons/m**2/s), respectively) indicating increased photosynthetic activity. In addition, increases in rETRmax (3.3-16.4 a.u.) and Ek (20-88 µmol photons/m**2/s) from December to May illustrates a higher potential for primary productivity as communities become better acclimated to under-ice light conditions. In conclusion, photosynthetic performance by ice algae (as assessed by PAM fluorometry) was tightly linked to sea ice salinity, temperature, and inorganic nutrient concentrations (mainly nitrogen).

Soil characteristics and decomposition of organic matter on Anchorage, Signy and Falkland Islands

Antarctic terrestrial ecosystems have poorly developed soils and currently experience one of the greatest rates of climate warming on the globe. We investigated the responsiveness of organic matter decomposition in Maritime Antarctic terrestrial ecosystems to climate change, using two study sites in the Antarctic Peninsula region (Anchorage Island, 67°S; Signy Island, 61°S), and contrasted the responses found with those at the cool temperate Falkland Islands (52°S). Our approach consisted of two complementary methods: (1) Laboratory measurements of decomposition at different temperatures (2, 6 and 10 °C) of plant material and soil organic matter from all three locations. (2) Field measurements at all three locations on the decomposition of soil organic matter, plant material and cellulose, both under natural conditions and under experimental warming (about 0.8 °C) achieved using open top chambers. Higher temperatures led to higher organic matter breakdown in the laboratory studies, indicating that decomposition in Maritime Antarctic terrestrial ecosystems is likely to increase with increasing soil temperatures. However, both laboratory and field studies showed that decomposition was more strongly influenced by local substratum characteristics (especially soil N availability) and plant functional type composition than by large-scale temperature differences. The very small responsiveness of organic matter decomposition in the field (experimental temperature increase <1 °C) compared with the laboratory (experimental increases of 4 or 8 °C) shows that substantial warming is required before significant effects can be detected.

Chemistry record of icecore BER11C95_25

A 181 m deep ice core drilled in 1994/95 on the south dome of Berkner Island, Antarctica, was analyzed for stable isotopes, major ions and microparticle concentrations. Samples for ion chromatography were prepared by using a novel technique of filling decontaminated sample from a device for continuous ice-core melting directly into the sample vials. The core was dated through identification of volcanic horizons and interpolative layer counting. The core, together with a similar core from the north dome, reveals a 1000 year history of relatively stable climate. Temporal variations in the two cores deviate from each other owing to changing patterns of regional-scale circulation; the best correspondence between them is found for MSA-. delta18O, accumulation rate and a sea-salt proxy show only negligible correlation, which suggests a complex meteorological setting. Increasing annual accumulation is observed for the last 100 years. A period of increased sea-salt concentrations started around AD 1405, as has also been observed in other cores. Microparticle concentrations are on average 1220 particles (>=1.0 ?m diameter)/mL; they are enhanced from AD 1200 to 1350, possibly because of a higher atmospheric mineral dust load or because local volcanic activity was stronger than previously thought. Microparticles and NH4+show marked but multiple and very irregular sub-annual peaks; long-term stacking of 1 year data intervals yields seasonal maxima in austral spring or mid-summer, respectively. Post-depositional redistribution was observed for MSA, NO3- and F- at volcanic horizons.

Effects of increased CO2 concentration on nutrient limited coastal summer plankton depend on temperature

Increasing seawater temperature and CO2 concentrations both are expected to increase coastal phytoplankton biomass and carbon to nutrient ratios in nutrient limited seasonally stratified summer conditions. This is because temperature enhances phytoplankton growth while grazing is suggested to be reduced during such bottom-up controlled situations. In addition, enhanced CO2 concentrations potentially favor phytoplankton species, that otherwise depend on costly carbon concentrating mechanisms (CCM). The trophic consequences for consumers under such conditions, however, remain little understood. We set out to experimentally explore the combined effects of increasing temperature and CO2 concentration for phytoplankton biomass and stoichiometry and the consequences for trophic transfer (here for copepods) on a natural nutrient limited Baltic Sea summer plankton community. The results show, that warming effects were translated to the next trophic level by switching the system from a bottom-up controlled to a mainly top-down controlled one. This was reflected in significantly down-grazed phytoplankton and increased zooplankton abundance in the warm temperature treatment (22.5°C). Additionally, at low temperature (16.5°C) rising CO2 concentrations significantly increased phytoplankton biomass. The latter effect however, was due to direct negative impact of CO2 on copepod nauplii which released phytoplankton from grazing in the cold but not in the warm treatments. Our results suggest that future seawater warming has the potential to switch trophic relations between phytoplankton and their grazers under nutrient limited conditions with the consequence of potentially disguising CO2 effects on coastal phytoplankton biomass.

Sediment and pore water geochemistry of sediment cores, Potter Cove, King George Island

Redox-sensitive trace metals (Mn, Fe, U, Mo, Re), nutrients and terminal metabolic products (NO3-, NH4+, PO43-, total alkalinity) were for the first time investigated in pore waters of Antarctic coastal sediments. The results of this study reveal a high spatial variability in redox conditions in surface sediments from Potter Cove, King George Island, western Antarctic Peninsula. Particularly in the shallower areas of the bay the significant correlation between sulphate depletion and total alkalinity, the inorganic product of terminal metabolism, indicates sulphate reduction to be the major pathway of organic matter mineralisation. In contrast, dissimilatory metal oxide reduction seems to be prevailing in the newly ice-free areas and the deeper troughs, where concentrations of dissolved iron of up to 700 µM were found. We suggest that the increased accumulation of fine-grained material with high amounts of reducible metal oxides in combination with the reduced availability of metabolisable organic matter and enhanced physical and biological disturbance by bottom water currents, ice scouring and burrowing organisms favours metal oxide reduction over sulphate reduction in these areas. Based on modelled iron fluxes we calculate the contribution of the Antarctic shelf to the pool of potentially bioavailable iron (Feb) to be 6.9x10**3 to 790x10**3 t/yr. Consequently, these shelf sediments would provide an Feb flux of 0.35-39.5/mg/m**2/yr (median: 3.8 mg/m**2/yr) to the Southern Ocean. This contribution is in the same order of magnitude as the flux provided by icebergs and significantly higher than the input by aeolian dust. For this reason suboxic shelf sediments form a key source of iron for the high nutrient-low chlorophyll (HNLC) areas of the Southern Ocean. This source may become even more important in the future due to rising temperatures at the WAP accompanied by enhanced glacier retreat and the accumulation of melt water derived iron-rich material on the shelf.

Molecular dissolved organic matter composition and environmental parameters from a laboratory incubation study

Dissolved organic matter (DOM) in the oceans constitutes a major carbon pool involved in global biogeochemical cycles. More than 96% of the marine DOM resists microbial degradation for thousands of years. The composition of this refractory DOM (RDOM) exhibits a molecular signature which is ubiquitously detected in the deep oceans. Surprisingly efficient microbial transformation of labile into RDOM was shown experimentally, implying that microorganisms produce far more RDOM than needed to sustain the global pool. By assessing the microbial formation and transformation of DOM in unprecedented molecular detail for 3 years, we show that most of the newly formed RDOM is molecularly different from deep sea RDOM. Only <0.4% of the net community production was channeled into RDOM molecularly undistinguishable from deep sea DOM. Our study provides novel experimentally derived molecular evidence and data for global models on the production, turnover and accumulation of marine DOM.

Evaluation of long chain 1,14-alkyl diols in marine sediments as indicators for upwelling and temperature

Long chain alkyl diols form a group of lipids occurring widely in marine environments. Recent studies have suggested several palaeoclimatological applications for proxies based on their distributions, but also revealed uncertainties about their applicability. Here we evaluate the use of long chain 1,14-alkyl diol indices for reconstruction of temperature and upwelling conditions by comparing index values, obtained from a comprehensive set of marine surface sediments, with environmental factors like sea surface temperature (SST), salinity and nutrient concentrations. Previous cultivation efforts indicated a strong effect of temperature on the degree of saturation and the chain length distribution of long chain 1,14-alkyl diols in Proboscia spp., quantified in the diol saturation index (DSI) and diol chain length index (DCI), respectively. However, values of these indices in surface sediments show no relationship with annual mean SST of the overlying water. It remains unknown what determines the DSI, although our data suggests that it may be affected by diagenesis, while the relationship between temperature and DCI may be different for different Proboscia species. In addition, contributions of algae other than Proboscia diatoms may affect both indices, although our data provide no direct evidence for additional long chain 1,14-alkyl diol sources. Two other indices using the abundance of 1,14-diols vs. 1,13-diols and C30 1,15-diols have previously been applied as indicators for upwelling intensity at different locations. The geographical distribution of their values supports the use of 1,14 diols vs. 1,13 diols [C28 + C30 1,14-diols]/[(C28 + C30 1,13-diols) + (C28 + C30 1,14-diols)] as a general indicator for high nutrient or upwelling conditions.

Chemistry of hot waters sampled from basaltic basement at DSDP Hole 83-504B

Seawater that has been altered by reaction with basaltic basement has been sampled from Deep Sea Drilling Project Hole 504B, located on 5.9-m.y.-old crust on the southern flank of the Costa Rica Rift. Fourteen water samples have been collected on Legs 69, 70, and 83, both before and after renewed drilling on the latter two legs, at temperatures from 69 to 133°C and pressures from 390 to 425 bars. The water sampled prior to renewed drilling on Leg 83 had occupied the hole for nearly 2 yr. since it was last flushed with surface seawater at the end of Leg 70. Despite some contamination by seawater during sampling, the composition of two of these waters has been determined by using nitrate as a tag for the contaminant. Both the 80 and 115°C waters have seawater chlorinity, but have lost considerable Mg, Na, K, sulfate, and 02, and have gained Ca, alkalinity, Si, NH3 and H2S. The loss of sulfate is due to anhydrite precipitation, as indicated by the d34S value of the remaining dissolved sulfate. The 87Sr/86Sr ratio has been lowered to 0.7086 for the 80°C water and 0.7078 for the 115°C water, whereas the Sr concentration is nearly unchanged. The changes in major element composition relative to seawater are also larger for the 115°C water, indicating that the basement formation water at this site probably varies in composition with depth. Based on their direction relative to seawater, the compositional changes for the 80 and 115°C waters do not complement the changes inferred for the altered rocks from Hole 504B, suggesting that the bulk composition of the altered rocks, like their mineralogy, is largely unrelated to the present thermal and alteration regime in the hole. The exact nature of the reacted seawaters cannot be determined yet, however. During its 2 yr. residence in the hole, the surface seawater remaining at the end of Leg 70 would have reacted with the wall rocks and exchanged with their interstitial formation waters by diffusion and possibly convection. How far these processes have proceeded is not yet certain, although calculations suggest that diffusion alone could have largely exchanged the surface seawater for interstitial water. The d18O of the samples is indistinguishable from seawater, however, and the d14C of the 80°C sample is similar to that of ocean bottom water. Although the interpretation of these species is ambiguous, that of tritium should not be. Tritium analyses, which are in progress, should clarify the nature of the reacted seawaters obtained from the hole.

Geochemistry of pore water and sediments from ODP Leg 136 sites

During Leg 136 drilling was conducted at two sites in pelagic sediments of the north central Pacific Ocean. In this report, pore-water analyses for major seawater constituents, alkalinity, ammonia, nitrate, phosphate, silica, Ba, Fe, Li, Mn, and Sr are presented. Although concentration gradients are generally weak, resulting from slow sedimentation and concomitant diffusive communication with overlying water, there is evidence of sediment/pore-water interactions, associated sediment diagenesis, and formation of authigenic minerals. Bulk major and trace element compositions of the sediments are consistent with reactions inferred to occur within the sediments and with the lithology and mineralogy. Elemental compositions of the sediments are not strongly affected by diagenesis and are primarily related to the dominant mineralogy. Sediments are typical of deep ocean pelagic settings with a significant contribution from the alteration of volcanic ash and the formation of zeolites. Sedimentary rare earth element patterns also provide evidence of active scavenging processes by Mn and Fe oxide phases in the deeper sediments at Site 842.