Glacial-interglacial seawater isotope change near the Chilean Margin as reflected by δ2H values of C37 alkenones

Stable hydrogen isotopic compositions of long-chain alkenones with 37 carbon atoms (δ2HC37) have been shown to reflect seawater salinity in culture and environmental studies, and this potential sea surface salinity proxy has been applied to several downcore records from different regions. However, previous studies were based solely on a single sediment core and often suggested unlikely large changes in salinity based on existing proxy calibrations. Here we present a new δ2HC37 record, in combination with oxygen isotopes of benthic foraminifera from the same samples, from a sediment core from the Chilean Margin (ODP Site 1235). The observed negative shift in δ2HC37 of 20 ‰ during the last deglaciation was identical to that of a previously published δ2HC37 record from the nearby, but deeper, ODP Site 1234, suggesting a regionally consistent shift in δ2HC37. This change translates into a negative hydrogen isotope shift in the surface seawater of ca. 14 ‰, similar to glacial-interglacial reconstructions based on other δ2HC37 records. The reconstructed bottom seawater oxygen isotope change based on benthic foraminifera during the last deglaciation is approximately -0.8 ‰, in line with previous studies. When translated into hydrogen isotopes of bottom seawater using the modern open-ocean water line, this would suggest a negative change of ca. 5 ‰, smaller than the reconstructed surface seawater shift based on alkenones. The larger change in surface water isotopes suggests that it experienced more freshening during the Holocene than bottom waters, either due to increased freshwater input, reduced evaporation, or a combination of the two

Exploration speed in captivity predicts foraging tactics and diet in free-living red knots

1. Variation in foraging tactics and diet is usually attributed to differences in morphology, experience and prey availability. Recently, consistent individual differences in behaviour (personality) have been shown to be associated with foraging strategies. Bolder or more exploratory individuals are predicted to have a faster pace‐of‐life and offset the costs of moving more or in risky areas, with higher energetic gains by encountering profitable foraging opportunities and prey. However, the relationship between personality, foraging and diet is poorly understood. 2. We investigated how exploratory behaviour in red knots Calidris canutus is associated with foraging tactics and diet by combining laboratory experiments, field observations and stable isotope analysis. First, we developed a mobile experimental arena to measure exploration speed in controlled settings. We validated the method by repeated testing of individuals over time and contexts. This setup allowed us to measure exploratory personality at the field site, eliminating the need to bring birds into captivity for long periods of time. After releasing birds within days of their capture, we asked whether exploration speed was associated with differences in foraging tactics and diet in the wild. 3. We found that tactile foraging red knots mainly caught hard‐shelled prey that are buried in the sediment, whereas visual foraging knots only captured soft preys located close to or on the surface. We also found that faster explorers showed a higher percentage of visual foraging than slower explorers. By contrast, morphology (bill length and gizzard size) had no significant effect on foraging tactics. Diet analysis based on δ(15)N and δ(13)C stable isotope values of plasma and red blood cells confirmed our field observations with slower explorers mainly consumed hard‐shelled prey while faster explorers consumed more soft than hard‐shelled prey. 4. Our results show that foraging tactics and diet are associated with a personality trait, independent of morphological differences. We discuss how consistent behaviour might develop early in life through positive feedbacks between foraging tactics, prey type and foraging efficiency

A multiproxy study of past environmental changes in the Sea of Okhotsk during the last 1.5 Ma

Long-chain diols have been detected in a wide range of environments and have been used to reconstruct past environmental changes, however only a few long-term records exist to date. Here we reconstructed past environmental changes in the central Sea of Okhotsk over the last 1.5 million years, covering the Mid-Pleistocene Transition (MPT). Sea surface temperatures (SST) reconstructed using the Long-Chain Diol Index (LDI) reflects glacial/interglacial changes. However, when compared with other organic paleothermometers (Uk′37 and TEXL86) the LDI-SST is lower during interglacials and similar or higher during glacials, possibly suggesting a shift of diol production season during interglacials. The LDI-SST does not change in periodicity around the MPT as observed for the TEXL86, likely due to this seasonal shift. Diatom productivity, as recorded by 1,14-diols and biogenic opal content, increased during the main deglaciations with a succession from Proboscia diatoms to diatoms with a more heavily silicified shell, confirming that primary productivity in the central Sea of Okhotsk is driven by sea-ice progress and retreat. In contrast to the LDI-SST, the 1,14-diols record shows a change in periodicity around the MPT from 41- to 100-kyr cycle, suggesting an influence of orbital parameters on diatom productivity. In the central Sea of Okhotsk, the relative amount of C32 1,15-diol (FC32 1,15), a proxy for riverine input, correlates with sea-level change with more riverine-derived material reaching the core site when the Amur River mouth is closer at lower sea-levels. In agreement, FC32 1,15 shows a change in periodicity during the MPT, with the appearance of a 100-kyr cycle. Our results show that the long chain diols can provide important paleoceanographic information in subpolar environments over long time scales, but that temperature reconstructions can be severely impacted by changes in seasonality

A stable isotope assay with 13C-labeled polyethylene to investigate plastic mineralization mediated by Rhodococcus ruber

Methods that unambiguously prove microbial plastic degradation and allow for quantification of degradation rates are necessary to constrain the influence of microbial degradation on the marine plastic budget. We developed an assay based on stable isotope tracer techniques to determine microbial plastic mineralization rates in liquid medium on a lab scale. For the experiments, 13C-labeled polyethylene (13C-PE) particles (irradiated with UV-light to mimic exposure of floating plastic to sunlight) were incubated in liquid medium with Rhodococcus ruber as a model organism for proof of principle. The transfer of 13C from 13C-PE into the gaseous and dissolved CO2 pools translated to microbially mediated mineralization rates of up to 1.2 % yr−1 of the added PE. After incubation, we also found highly 13C-enriched membrane fatty acids of R. ruber including compounds involved in cellular stress responses. We demonstrated that isotope tracer techniques are a valuable tool to detect and quantify microbial plastic degradation

Alkenone Distributions and Hydrogen Isotope Ratios Show Changes in Haptophyte Species and Source Water in the Holocene Baltic Sea

The Baltic Sea, a dynamic, marginal marine basin, experienced a number of large changes in salinity during the Holocene as a result of fluctuations in global and local sea level related to melting of glacial ice sheets and subsequent isostatic rebound. These changes likely had pronounced effects on the species composition of haptophytes, a common phytoplankton group found in the Baltic Sea. This dynamic environment provides the ideal setting to study how species change impacts distribution and hydrogen isotope ratios of long‐chain alkenones (δ²H_(C37)), haptophyte‐specific biomarkers. Here we analyzed the aforementioned parameters in Holocene sediments covering the contrasting hydrological phases of the Baltic Sea. Alkenone distributions changed with different Baltic Sea salinity phases, suggesting that species shifts coincide with salinity change. δ²H_(C37) values show two major shifts: one in the middle of the freshwater Ancylus Lake phase (10.6 to 7.7 ka) and a second at the transition from the brackish Littorina Sea phase (7.2 to 3 ka) into the fresher Modern Baltic (3 ka to the present). The first shift represents a significant enrichment of 50‰, which cannot be explained by salinity or species changes only. At this time, the isotopically depleted ice sheets had melted, and only the relatively enriched freshwater source remained. The second shift, coincident with a change in distribution, is likely caused by a change in species composition alone. These findings show that hydrogen isotope ratios of long‐chain alkenones, combined with their relative distribution, can be used to reconstruct changes in source water

Algal biomarkers as a proxy for pCO2: Constraints from late Quaternary sapropels in the eastern Mediterranean

Records of carbon dioxide concentrations (partial pressure expressed as pCO2) over Earth’s history provide trends that are critical to understand our changing world. To better constrain pCO2 estimations, here we test organic pCO2 proxies against the direct measurements of pCO2 recorded in ice cores. Based on the concept of stable carbon isotopic fractionation due to photosynthetic CO2 fixation (Ɛp), we use the stable carbon isotopic composition (δ13C) of the recently proposed biomarker phytol (from all photoautotrophs), as well as the conventionally used alkenone biomarkers (from specific species) for comparison, to reconstruct pCO2 over several Quaternary sapropel formation periods (S1, S3, S4, and S5) in the eastern Mediterranean Sea. The reconstructed pCO2 values are within error of the ice core values but consistently exceed the ice core values by ca. 100 µatm. This offset corresponds with atmospheric disequilibrium of present day CO2[aq] concentrations in the Mediterranean Sea from global pCO2, equivalent to ca. 100 µatm, although pCO2 estimates derived from individual horizons within each sapropel do not covary with the ice core values. This may possibly be due to greater variability in local CO2[aq] concentration changes in the Mediterranean, as compared with the global average pCO2, or possibly due to biases in the proxy, such as variable growth rate or carbon-concentrating mechanisms. Thus, the offset is likely a combination of physiological or environmental factors. Nevertheless, our results demonstrate that alkenone- and phytol-based pCO2 proxies yield statistically similar estimations (P-value = 0.02, Pearson’s r-value = 0.56), and yield reasonable absolute estimations although with relatively large uncertainties (± 100 µatm)

Evidence for substantial intramolecular heterogeneity in the stable carbon isotopic composition of phytol in photoautotrophic organisms

Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Organic Geochemistry 39 (2008): 135-146, doi:10.1016/j.orggeochem.2007.09.002.The ubiquitous isoprenoid phytol was isolated from a range of algae, terrestrial plants and a bacterium and its two terminal carbon atoms were quantitatively removed by chemical oxidation. The product, 6,10,14-trimethylpentadecan-2-one, was depleted in 13C by 1-4‰ relative to the parent phytol. This difference is significant, and indicates that the pathway for biosynthesis of phytol induces substantial intramolecular stable carbon isotopic fractionations. The nature and magnitude of the fractionations suggest strongly that it is associated both with the biosynthesis of isopentenyl pyrophosphate via the 2-C-methylerythritol-4-phosphate pathway and with the formation of carotenoids and phytol from geranyl-geraniolphosphate. As a result of these large, intramolecular isotopic differences, diagenetic products formed by loss of C, such as pristane, may be naturally depleted in 13C by several permil relative to phytane.Shell International Petroleum Maatschappij BV is thanked for financial support for the irm- GC-MS facilit