Flat meridional temperature gradient in the early Eocene in the subsurface rather than surface ocean

The early Eocene (49–55 million years ago) is a time interval characterized by elevated surface temperatures and atmospheric CO2 (refs 1,2), and a flatter-than-present latitudinal surface temperature gradient3, 4. The multi-proxy-derived flat temperature gradient has been a challenge to reproduce in model simulations5, 6, 7, especially the subtropical warmth at the high-latitude surface oceans4, 8, inferred from the archaeal lipid-based palaeothermometry, . Here we revisit the interpretation by analysing a global collection of multi-proxy temperature estimates from sediment cores spanning millennia to millions of years. Comparing the variability between proxy types, we demonstrate that the present interpretation9 overestimates the magnitude of past climate changes on all timescales. We attribute this to an inappropriate calibration, which reflects subsurface ocean but is calibrated to the sea surface, where the latitudinal temperature gradient is steeper. Recalibrating the proxy to the temperatures of subsurface ocean, where the signal is probably formed, yields colder -temperatures and latitudinal gradient consistent with standard climate model simulations of the Eocene climate10, invalidating the apparent, extremely warm polar sea surface temperatures. We conclude that there is a need to reinterpret -inferred marine temperature records in the literature, especially for reconstructions of past warm climates that rely heavily on this proxy as reflecting subsurface ocean

Archaeal membrane lipid-based paleothermometry for applications in polar oceans

CITATION: Fietz, S., Ho, S. L. & Huguet, C. 2020. Archaeal membrane lipid-based paleothermometry for applications in polar oceans. Oceanography, 33(2):104–114, doi:10.5670/oceanog.2020.207.The original publication is available at https://tos.orgTo establish whether ongoing climate change is outside the range of natural variability and a result of anthropogenic inputs, it is essential to reconstruct past oceanic and atmospheric temperatures for comparison with the modern world. Reconstructing past temperatures is a complex endeavor that employs indirect proxy indicators. Over the past two decades, promising paleothermometers have been developed that use isoprenoidal glycerol dialkyl glycerol tetraethers (isoGDGTs) from the membrane lipids of archaea preserved in marine sediments. These proxies are based on the observed relationship between lipid structure and temperature. As with all proxy indicators, observed relationships are often complex. Here, we focus on the application of isoGDGT paleotemperature proxies in the polar oceans, critical components of the global climate system. We discuss the application of and caveats regarding these archaeal membrane lipid-derived proxies and make recommendations to improve isoGDGT-derived polar ocean temperature reconstructions. We also review initial successes using hydroxylated (OH) isoGDGTs proxies in cold Arctic and Southern Ocean regions and recommend that multi-proxy approaches, including both hydroxylated and non-hydroxylated isoGDGTs, be used to contribute to the robustness of paleotemperature reconstructions.Publisher's versio

Estimating bioturbation from replicated small-sample radiocarbon ages.

Marine sedimentary records are a key archive when reconstructing past climate; however, mixing at the seabed (bioturbation) can strongly influence climate records, especially when sedimentation rates are low. By commingling the climate signal from different time periods, bioturbation both smooths climate records, by damping fast climate variations, and creates noise when measurements are made on samples containing small numbers of individual proxy carriers, such as foraminifera. Bioturbation also influences radiocarbon-based age-depth models, as sample ages may not represent the true ages of the sediment layers from which they were picked. While these effects were first described several decades ago, the advent of ultra-small-sample 14C dating now allows samples containing very small numbers of foraminifera to be measured, thus enabling us to directly measure the age-heterogeneity of sediment for the first time. Here, we use radiocarbon dates measured on replicated samples of 3-30 foraminifera to estimate age-heterogeneity for five marine sediment cores with sedimentation rates ranging from 2-30 cm / kyr. From their age-heterogeneities and sedimentation rates we infer mixing depths of 10-20 cm for our core sites. Our results show that when accounting for age-heterogeneity, the true error of radiocarbon dating can be several times larger than the reported measurement. We present estimates of this uncertainty as a function of sedimentation rate and the number of individuals per radiocarbon date. A better understanding of this uncertainty will help us to optimise radiocarbon measurements, construct age models with appropriate uncertainties and better interpret marine paleo records

Challenges and potential in the interpretation of global temperature proxy data compilations

As the availability of high-resolution proxy records increases, the number of large-scale compilations that are built and analyzed continues to grow. Such datasets allow us to disentangle regional and global climate changes from local and proxy specific effects, to better bridge the spatial scales of local proxy recorders vs. global climate models and they support more objective statistical analyses. However, compilations also often combine data for multiple proxy types and which may record different climate variables (e.g. different seasonal or atmospheric vs. water temperatures). Datasets may also vary in quality, and compilations often ignore the expert knowledge of the authors of the original individual paleoclimate datasets as well as site-specific and proxy-specific effects. Here I review current and recent studies that have used global compilations of temperature related proxy data to infer the glacial and Holocene climate evolution and the temporal and spatial structures of climate variability. I demonstrate how the analysis of large-scale compilations can not only improve our knowledge of the evolution of past climate but also provide insight into the potential and limitations of specific paleoclimate proxies and emphasize the importance of realistic uncertainty estimates

Sensitivity of clumped isotope temperatures in fossil benthic and planktic foraminifera to diagenetic alteration

Applying the clumped isotope (Δ47) thermometer to foraminifer microfossils offers the potential to significantly improve paleoclimate reconstructions, owing to its insensitivity to the isotopic composition of seawater (unlike traditional oxygen isotope (δ18O) analyses). However, the extent to which primary Δ47 signatures of foraminiferal calcites can be overprinted during diagenesis is not well known. Here, we present Δ47 data as well as high-resolution (∼10 kyr) δ18O and δ13C middle Eocene time series, measured on benthic and planktic foraminifera from ODP/IODP Sites 1408, 1409, 1410, 1050, 1260 and 1263 in the Atlantic Ocean. The sites examined span various oceanographic regimes, including the western tropical to mid-latitude North Atlantic, and the eastern mid-latitude South Atlantic. Comparing data from contemporaneous foraminifera with different preservation states, we test the effects of diagenetic alteration on paleotemperature reconstructions for the deep and surface ocean. We find that overall, primary Δ47 signatures appear similarly sensitive to diagenetic overprinting as δ18O, with differences in sensitivity depending on pore fluid chemistry and the amount of secondary calcite. Where planktic foraminifera are significantly altered, sea surface temperatures derived from Δ47 and δ18O values are biased towards cool temperatures. In comparison, Δ47 and δ18O values of benthic and well preserved planktic foraminifera are less affected by diagenesis and thus likely to yield robust foraminiferal calcification temperatures. With independent estimates of diagenetic calcite fractions, secondary overprints could be corrected for, using end-member modeling and Δ47-based temperatures from benthic foraminifera

Consumer personality, privacy concerns and usage of location-based services (LBS)

This paper examines the effects of the Big Five personality traits on concern for information privacy (CFIP) and the effects of the formulated concern for information privacy towards perceived risk, which in turn determine location-based services (LBS) usage intention. Data for this research was collected from 291 users and non-users of LBS. Result from Pearson correlation analysis indicated significant relationships exist between: (1) extraversion, and openness with collection; (2) extraversion, conscientiousness, and openness with improper access; (3) extraversion, conscientiousness, and openness with errors; (4) agreeableness, neuroticism, and openness with secondary use. All four dimensions of CFIP are found to have a significant direct relationship with perceived risk of using LBS. Implications for research and practice for location-based service providers are discussed

Molecular cloning, gene expression profiling and in silico sequence analysis of vitamin E biosynthetic genes from the oil palm

Homogentisate geranylgeranyl transferase (HGGT) and homogentisate phytyltransferase (HPT) are the two key enzymes involved in condensation of homogentisic acid (HGA) with a prenyldiphosphate to produce tocotrienols and tocopherols in plants, respectively. The partial cDNAs encoding HGGT and HPT enzymes were successfully isolated from the two oil palm species, Elaeis guineensis and Elaeis oleifera by PCR amplification using degenerate primers. Subsequently, full length cDNA sequences were completed by rapid amplification of cDNA ends (RACE) and further annotated using various bioinformatics tools. The analysis revealed the presence of an UbiA prenyltransferase conserved domain in all four deduced amino acid sequences and suggested that oil palm HGGT and HPT are more evolutionarily related to their counterparts from other monocot plant species. Quantitative gene expression analysis was carried out to elucidate the transcript profiles of the oil palm HGGT and HPT in different oil palm tissues and at different developmental stages of the mesocarp. The HPT was constitutively expressed in all analyzed tissues except in 15 w.a.a kernel whereas oil palm HGGT showed preferential expression in mesocarp and kernel tissues. However, HPT was highly expressed at the fruit ripening stage of 17 w.a.a mesocarp when active oil deposition occurs. Genome-walking PCR successfully amplified the promoter regions of HGGT and HPT from E. guineensis. Computational analysis using PlantCare and PLACE databases revealed several cis-regulatory elements including phytohormone-responsive, light-responsive and abiotic factor-responsive elements which may be involved in coordinating expression of both genes. Taken together, this study provides useful information about important features of the cDNA and promoter sequences as well as an insight into the transcriptional regulation of these key vitamin E genes for future genetic improvement efforts

Stable Biological Production in the Eastern Equatorial Pacific Across the Plio-Pleistocene Transition (∼3.35–2.0 Ma)

Upwelling within the Eastern Equatorial Pacific (EEP) Ocean is a key factor for the Earth's climate because it supports >10% of the present-day biological production. The dynamics of upwelling in the EEP across the Plio-Pleistocene transition—an interval particularly relevant for understanding near-future warming due to Anthropocene-like atmospheric carbon-dioxide levels—have been intensively studied for the region east of the East Pacific Rise. In contrast, changes of the equatorial upwelling regime in the open Pacific Ocean west of this oceanographic barrier have received markedly less attention. We therefore provide new proxy records from Ocean Drilling Program Site 849 located within the EEP open-ocean upwelling regime. Our target interval (∼3.35–2.0 Ma) covers the Plio-Pleistocene transition characterized by the intensification of Northern Hemisphere Glaciation (iNHG). We use benthic δ18O values to generate a new, high-resolution age model for Site 849, and sand-accumulation rates together with benthic δ13C values to evaluate net export production. Although showing temporary substantial glacial-interglacial variations, our records indicate stability in net export production on secular timescales across the iNHG. We suggest the following processes to have controlled the long-term evolution of primary productivity at Site 849. First, nutrient export from the high latitudes to the EEP; second, a successive shoaling of the Pacific nutricline during the studied interval; and third, a simultaneous reduction in dust-borne iron input.publishedVersio