ALBERT

Description: Reconstructed sea surface temperatures (SSTs) derived from Mg/Ca measurements in nine encrusting coralline algal skeletons from the Aleutian archipelago in the northernmost Pacific Ocean reveal an overall increase in SST from 1665 to 2007. In the Aleutian SST reconstruction, decadal-scale variability is a transient feature present during the 1700s and early 1800s and then fully emerging post-1950. SSTs vary coherently with available instrument records of cyclone variance and vacillate in and out of coherence with multicentennial Pacific Northwest drought reconstructions as a response to SST-driven alterations of storm tracks reaching North America. These results indicate that an influence of decadal-scale variability on the North Pacific storm tracks only became apparent during the midtwentieth century. Furthermore, what has been assumed as natural variability in the North Pacific, based on twentieth century instrumental data, is not consistent with the long-term natural variability evident in reconstructed SSTs predating the anthropogenic influence.

Description: While recent changes in subarctic North Pacific climate had dramatic effects on ecosystems and fishery yields, past climate dynamics and teleconnection patterns are poorly understood due to the absence of century-long high-resolution marine records. We present the first 117-year long annually resolved marine climate history from the western Bering Sea/Aleutian Island region using information contained in the calcitic skeleton of the long-lived crustose coralline red alga Clathromorphum nereostratum, a previously unused climate archive. The skeletal δ18O-time series indicates significant warming and/or freshening of surface waters after the middle of the 20th century. Furthermore, the time series is spatiotemporally correlated with Pacific Decadal Oscillation (PDO) and tropical El Niño-Southern Oscillation (ENSO) indices. Even though the western Bering Sea/Aleutian Island region is believed to be outside the area of significant marine response to ENSO, we propose that an ENSO signal is transmitted via the Alaskan Stream from the Eastern North Pacific, a region of known ENSO teleconnections.

Description: Blue mussel individuals (Mytilus edulis) were cultured at four different salinities (17, 20, 29, and 34). During the course of the experiment, temperature was gradually increased from 6°C to 14°C. Mg/Ca and Sr/Ca ratios of the shell calcite portions produced during the 9 weeks of experimental treatment as well parts that were precipitated before the treatment phase were measured by laser ablation–multicollector–inductively coupled plasma–mass spectrometry. Mg/Ca ratios show a positive correlation with temperature for individuals cultured at salinity 29 and 34 (Mg/Ca (mmol/mol) ∼ (0.2–0.3)*T (°C)), while for individuals cultured at low salinities (17, 20) no trend was observed. Sr/Ca ratios were not affected by temperature but strongly by salinity. The data show very strong biological influence (“individual differences” and “physiological variability”) on elemental ratios (79% on Mg/Ca and 41% on Sr/Ca) in M. edulis calcite. The results challenge the use of blue mussel shell data as environmental proxies.

Description: In this study we present the first combined investigation into the composition of the major matrices involved in calcification processes (surrounding water, extrapallial fluid, aragonite, and calcite) of Mytilus edulis with respect to their calcium isotope (d44/40Ca) and elemental compositions (Sr/Ca and Mg/Ca). Our aim was to examine the suitability of Mytilus edulis as a proxy archive and to contribute to the understanding of the process of biomineralization. Mytilus edulis specimens were live collected from the Schwentine Estuary, Kiel Fjord, and North Sea (Sylt). d44/40Ca was determined by thermal ionization mass spectrometry (TIMS) accompanied by measurements of Mg/Ca and Sr/Ca using inductively coupled plasma–optical emission spectroscopy (ICP-OES). The elemental and isotopic compositions of the investigated matrices showed systematic offsets. The carbonates are strongly depleted in their magnesium and strontium concentrations and fractionated toward lighter calcium isotope compositions relative to the surrounding Schwentine Estuary water. The opposite is observed for the extrapallial fluid (EPF). Our findings extend the results of previous studies reporting a strong biological control and the interaction of different environmental conditions influencing biomineralization. Future studies should focus on the temporal development of the interrelation between the different matrices.

Description: New U-series isotope data for lavas from the East Scotia backarc spreading center span a large range in (230Th/232Th) and (238U/232Th). Most of the backarc lavas have (238U/230Th) 〈 1, similar to the composition of mid-oceanic-ridge basalts (MORB). Lavas from two segments have (238U/230Th) 〉 1 and are enriched in fluid-mobile elements, implying a recent addition of a U-rich slab-derived component. The data from one segment suggest an influence from an aqueous fluid from altered MORB, whereas samples from the other slab-influenced segment show addition of a sediment melt. The slab-influenced samples form a distinct trend in the equiline diagram between aqueous fluid and sediment melt that is suggested to be a mixing line rather than an isochron.

Description: Stable strontium isotopes (here 88Sr/86Sr) are introduced as a new member of the nontraditional stable isotopes. We have developed a bracketing standard method for the determination of δ88/86Sr using an AXIOM MC-ICP-MS and normalizing to strontium SRM NBS987. For individual measurements the external reproducibility is better than about 25 ppm (1σ RSD). For the IAPSO seawater standard a δ88/86Sr value of 0. 381 ± 0.010‰ (2SEM) was determined. For the first time a temperature-dependent strontium isotope fractionation during calcium carbonate precipitation could be shown. Aragonite samples inorganically precipitated under temperature control between 10 and 50°C revealed a δ88/86Sr/temperature dependency of 0.0054(5)‰/°C (R2 = 0.987). In contrast, for natural coral samples (Pavona clavus) from a proxy calibration study (23 to 27°C) we did determine 0.033(5)‰/°C (R2 = 0.955). The processes causing this sixfold stronger temperature dependency for the natural coral samples have to be studied in more detail in future studies. In a first approach the different slopes can be interpreted as effects of kinetic fractionation of strontium ions with or without a hydrate shell of 22 to 29 water molecules.

Description: Lead (Pb), neodymium (Nd), and strontium (Sr) isotopic analyses were carried out on sediment leachates (reflecting the isotope composition of past seawater) and digests of the bulk residues (reflecting detrital continental inputs) of Integrated Ocean Drilling Program (IODP) Leg 302 and core PS2185 from the Lomonosov Ridge (Arctic Ocean). Our records are interpreted to reflect changes in continental erosion and oceanic circulation, driven predominantly by tectonic forcing on million-year timescales in the older (pre-2 Ma) part of the record and by climatic forcing of weathering and erosion of the Eurasian continental margin on thousand-year timescales in the younger (post-2 Ma) part. These data, covering the past ∼15 Ma, show that continental inputs to the central Arctic Ocean have been more closely linked to glacial and hydrological processes occurring on the Eurasian margin than on continental North America and Greenland. The constancy of the detrital input signatures supports the early existence of an Arctic sea ice cover, whereas the major initiation of Northern Hemisphere glaciation at 2.7 Ma appears to have had little impact on the weathering regime of the Eurasian continental margin.

Description: Precisely quantifying the current climate-related sea level change requires accurate knowledge of long-term geological processes known as Glacial Isostatic Adjustments (GIA). Although the major postglacial melting phase is likely to have ended ∼6–4 ka BP (before present), GIA is still significantly affecting the present-day vertical position of the mean sea surface and the sea bottom. Here we present empirical rsl (relative sea level) data based on U/Th dated fossil corals from reef platforms of the Society Islands, French Polynesia, together with the corresponding GIA-modeling. Fossil coral data constrain the timing and amplitude of rsl variations after the Holocene sea level maximum (HSLM). Upon correction for isostatic island subsidence, we find that local rsl was at least ∼1.5 ± 0.4 m higher than present at ∼5.4 ka. Later, minor amplitude variations occurred until ∼2 ka, when the rsl started dropping to its present position with a rate of ∼0.4 mm/yr. The data match with predicted rsl curves based on global ice-sheet chronologies confirming the role of GIA-induced ocean siphoning effect throughout the mid to late Holocene. A long lasting Late Holocene highstand superimposed with second-order amplitudinal fluctuations as seen from our data suggest that the theoretical predicted timing of rsl change can still be refined pending future calibration.

Description: Mytilus edulis were cultured for 3 months under six different seawater pCO(2) levels ranging from 380 to 4000 mu atm. Specimen were taken from Kiel Fjord (Western Baltic Sea, Germany) which is a habitat with high and variable seawater pCO(2) and related shifts in carbonate system speciation (e. g., low pH and low CaCO3 saturation state). Hemolymph (HL) and extrapallial fluid (EPF) samples were analyzed for pH and total dissolved inorganic carbon (C-T) to calculate pCO(2) and [HCO3-]. A second experiment was conducted for 2 months with three different pCO(2) levels (380, 1400 and 4000 mu atm). Boron isotopes (delta B-11) were investigated by LA-MC-ICP-MS (Laser Ablation-Multicollector-Inductively Coupled Plasma-Mass Spectrometry) in shell portions precipitated during experimental treatment time. Additionally, elemental ratios (B/Ca, Mg/Ca and Sr/Ca) in the EPF of specimen from the second experiment were measured via ICP-OES (Inductively Coupled Plasma-Optical Emission Spectrometry). Extracellular pH was not significantly different in HL and EPF but systematically lower than ambient water pH. This is due to high extracellular pCO(2) values, a prerequisite for metabolic CO2 excretion. No accumulation of extracellular [HCO3-] was measured. Elemental ratios (B/Ca, Mg/Ca and Sr/Ca) in the EPF increased slightly with pH which is in accordance with increasing growth and calcification rates at higher seawater pH values. Boron isotope ratios were highly variable between different individuals but also within single shells. This corresponds to a high individual variability in fluid B/Ca ratios and may be due to high boron concentrations in the organic parts of the shell. The mean delta B-11 value shows no trend with pH but appears to represent internal pH (EPF) rather than ambient water pH.

Description: The origin of coastal and high-elevation marine gravels on the Hawaiian islands of Lanai and Molokai is controversial, because the vertical tectonics of these islands is poorly constrained. The gravels are either from eustatic highstands or were left by massive tsunamis from offshore giant landslides. In contrast, at Kohala on the island of Hawaii, where continuous subsidence is well established, lithofacies analysis and dating of a fossiliferous marine conglomerate 1.5–61 m above present sea level support a tsunami origin and indicate a runup of 〉400 m 〉6 km inland. The conglomerate age, 110 ± 10 ka, suggests a tsunami caused by the ca. 120 ka giant Alika 2 landslide from nearby Mauna Loa volcano.