Proxy For Seawater Temperature Research Articles

Descriptive Capability of Datasets as Proxy of Sea Water Temperature in Coastal Systems: An Evaluation from the Aegean Sea

Scientific and technological progresses have introduced diverse data sources for seawater temperature over broad temporal and spatial ranges. Here, we investigated the performance of satellite and model-based seawater temperature data for different temporal composites and depths. We applied an in-situ temperature time-series obtained in a coastal bottom in the Aegean Sea over three years, as the reference. Both datasets showed largely significant relationships based on cross-correlation analyses and presented descriptive properties of the in-situ conditions at corresponding depths. Based on the results of analyses, the modeling datasets presented more reliable results and representations of in-situ conditions than the datasets obtained from satellite for the coastal region. However, the datasets obtained from the satellite also provided reliable data for all time frames investigated, particularly in the mixed surface layer. Monthly datasets were more effective in providing descriptive values in long term studies. This is the first detailed study to explore the descriptive capacities of modeling for water temperature in coastal environments. According to the results, the selection of a dataset as a proxy for seawater temperature requires careful consideration. The present study provides an extensive baseline for evaluating the suitability of the application of specific datasets as proxies in coastal ecosystems.

Comparing Seawater Temperature Proxy Records for the Past 90 Myrs From the Shallow Shelf Record Bass River, New Jersey

AbstractWe present a multiproxy (foraminifer Mg/Ca, δ18O, ∆47, and Sr/Ca, and biomarker TEX86H, MATmrs) low‐resolution paleotemperature record based on seven sets of high‐resolution time series from the late Cretaceous to Miocene from the Ocean Drilling Program Bass River site, New Jersey Shelf, North Atlantic. Along with insight into long‐term climate evolution, this allows testing for internal consistency between proxies. The bottom water temperatures (BWTs) reconstructed using benthic δ18O and Mg/Ca values show good agreement in recorded trends with the TEX86H sea surface and shallow subsurface temperature record, and with the stacked global benthic oxygen isotope record. The Mg/Ca‐based BWTs are higher than the δ18O‐based BWTs, likely due to uncertainty in the assumptions associated with the Mg/Ca calibration to seawater Mg/Ca. Absolute δ18O‐based BWT reconstructions are supported by clumped isotope paleothermometry. The agreement in main trends of the independent paleotemperature proxies indicates that the underlying assumed mechanisms for the different proxy relations to temperature stayed largely intact back to at least 90 Ma. Consistent differences in absolute temperature values highlight, however, that a better understanding of the individual proxies is required in order to achieve accurate absolute temperature reconstructions

Oceanographic moorings as year-round laboratories for investigating growth performance and settlement dynamics in the Antarctic scallop Adamussium colbecki (E. A. Smith, 1902).

BackgroundOceanographic moorings (OMs) are standard marine platforms composed of wires, buoys, weights and instruments, and are used as in situ observatories to record water column properties. However, OMs are also comprised of hard substrates on which a variety of invertebrates can settle when they encounter these structures along their dispersal routes. In this contribution, we studied the fouling communities found on two OMs deployed in the Ross Sea (Antarctica). Furthermore, a cage containing the Antarctic scallop Adamussium colbecki (E. A. Smith, 1902) was incorporated in the OM. The growth of the caged A. colbecki were evaluated after 1 year and their shells used as biological proxy for seawater temperature and salinity.MethodsA variety of settlers were collected from two different OMs deployed in the Ross Sea (Antarctica) and species identified using a combination of morphological and genetic (mainly through DNA barcoding) characteristics. Caged scallops were individually marked with permanent tags and their growth studied in terms of size-increment data (SID). Cages were specifically designed to prevent damage to individuals due to water drag during OM deployment and retrieval. Growth parameters from the caged individuals were applied to the A. colbecki juveniles that had settled on the mooring, to trace the likely settlement period.ResultsThe growth performance of caged A. colbecki was similar to that from previous growth studies of this species. The remarkable survival rate of caged specimens (96.6%) supports the feasibility of caging experiments, even for a species with a fragile shell such as the Antarctic scallop. Some of the new recruits found on the mooring were A. colbecki, the same species we put into special cages fixed to it. The settlement of the A. colbecki juveniles started during the Austral spring with a peak in summer months and, remarkably, coincided with seasonal changes in water temperature and flow direction, which were recorded by the mooring’s instruments. Genetic data from other settlers provided new information about their larval ecology and connectivity.DiscussionOceanographic moorings are expensive and complex experimental platforms that, at present, are strictly used for the acquisition of physical and biogeochemical data. Their use for in situ ecological experiments on model organisms suitable for caging and to study fouling species has yet to be fully explored. We present the outcomes of a study, which represents a baseline for the characterization of Antarctic fouling biodiversity. We hope that in the near future an internationally coordinated systematic study of settlers could be initiated around the Antarctic continent. This could utilize “new generation OMs” equipped with standardized settlement structures and agreed sampling protocols for the study of fouling communities.

The effects of environment on <i>Arctica islandica</i> shell formation and architecture

Abstract. Mollusks record valuable information in their hard parts that reflect ambient environmental conditions. For this reason, shells can serve as excellent archives to reconstruct past climate and environmental variability. However, animal physiology and biomineralization, which are often poorly understood, can make the decoding of environmental signals a challenging task. Many of the routinely used shell-based proxies are sensitive to multiple different environmental and physiological variables. Therefore, the identification and interpretation of individual environmental signals (e.g., water temperature) often is particularly difficult. Additional proxies not influenced by multiple environmental variables or animal physiology would be a great asset in the field of paleoclimatology. The aim of this study is to investigate the potential use of structural properties of Arctica islandica shells as an environmental proxy. A total of 11 specimens were analyzed to study if changes of the microstructural organization of this marine bivalve are related to environmental conditions. In order to limit the interference of multiple parameters, the samples were cultured under controlled conditions. Three specimens presented here were grown at two different water temperatures (10 and 15 °C) for multiple weeks and exposed only to ambient food conditions. An additional eight specimens were reared under three different dietary regimes. Shell material was analyzed with two techniques; (1) confocal Raman microscopy (CRM) was used to quantify changes of the orientation of microstructural units and pigment distribution, and (2) scanning electron microscopy (SEM) was used to detect changes in microstructural organization. Our results indicate that A. islandica microstructure is not sensitive to changes in the food source and, likely, shell pigment are not altered by diet. However, seawater temperature had a statistically significant effect on the orientation of the biomineral. Although additional work is required, the results presented here suggest that the crystallographic orientation of biomineral units of A. islandica may serve as an alternative and independent proxy for seawater temperature.

Exploring the oxygen and carbon isotopic composition of the Mediterranean red coral (Corallium rubrum) for seawater temperature reconstruction

Here we provide first evidence that the stable oxygen and carbon isotopic composition (δ18O, δ13C) of the high-magnesium calcite skeleton red coral Corallium rubrum can be used as a reliable seawater temperature proxy. This is based upon the analyses of living colonies of C. rubrum from different depths and localities in the Western Mediterranean Sea. The assessment of the growth rates has been established through the analysis of growth band patterns. The δ18O and δ13C compositions show large variability with a significant difference between the branches and the bases of the colonies. In both coral portions, the δ18O and δ13C values are highly correlated and show well-defined linear trends. Following the “lines technique” approach developed by Smith et al. (2000) for scleractinian aragonitic deep-water corals, our data have been combined with published values for the deep-sea gorgonian corals Isididae and Coralliidae from Kimball et al. (2014) and Hill et al. (2011) resulting in the following δ18O temperature equation:T°C=−5.05±0.24×δ18Ointercept+14.26±0.43R2=0.962pvalue<0.0001The error associated with this equation is ±0.5°C at the mean temperature of the data set, ±0.7°C for corals living in 2°C water and ±1°C for coral living in warmer water (17°C).The highly significant δ18Ointercept vs. temperature relationship combined with the “lines technique” method can be reliably applied to the calcitic skeleton to obtain calcification temperature estimates in the past, although this approach requires the knowledge of the past δ18O and δ13C composition of seawater and it is labor and time intensive.

Mg/Ca thermometry in planktic foraminifera: Improving paleotemperature estimations for G. bulloides and N. pachyderma left

AbstractPlanktic foraminiferal Mg/Ca ratios have become a fundamental seawater temperature proxy in past climate reconstructions, due to the temperature dependence of Mg uptake into foraminiferal calcite. However, empirical calibrations for single species from methodologically consistent data are still lacking. Here we present species‐specific calibrations of Mg/Ca versus calcification temperature for two commonly used species of planktic foraminifera: Globigerina bulloides and Neogloboquadrina pachyderma left, based on a series of Southern Ocean and North Atlantic core tops. Combining these new data with previously published data, we derive an integrated G. bulloides Mg/Ca‐temperature calibration for mid and high latitudes of both hemispheres between 2 and 18°C, where Mg/Ca = 1.006 ± 0.032 * e0.065 ± 0.003*Tiso (R2 = 0.82). G. bulloides is found to calcify deeper in the Southern Ocean (∼ 200 m) than in the North Atlantic (top 50 m). We also propose a Mg/Ca temperature calibration to describe the temperature response in N. pachyderma left that calcified away from the influence of sea ice in the Southern Ocean, valid between ∼ −1 and 9°C, of the form Mg/Ca = 0.580 ± 0.016 * e0.084 ± 0.006*Tiso (R2 = 0.70). These calibrations account for uncertainties on Mg/Ca measurements and calcification temperature that were carefully estimated and propagated using Monte Carlo iterations. The 1σ propagated error in Mg/Ca‐derived temperatures is 1.1°C for G. bulloides and 0.9°C for N. pachyderma left for the presented data sets. Geographical extension of genotypes must be assessed when choosing to develop regional or global calibrations.

The effect of improved chromatography on GDGT-based palaeoproxies

The development of methods using liquid chromatography coupled to mass spectrometry to analyze glycerol dialkyl glycerol tetraethers (GDGTs) has substantially expanded the biomarker tool box and led to the development of several new proxies. Recent studies have shown that new high performance liquid chromatography methods have substantially improved separation of GDGT isomers and detection of novel isomers. Here we present a chromatographic method based on two ultra-high performance liquid chromatography silica columns capable of separating a wide range of GDGTs with good resolution and which compares favorably with previously published methods. This method was tested on a part of the global calibration set of the TEX86, a proxy for sea water temperature, and on a part of the global calibration set of the MBT5Me, a proxy for air temperature, and CBT′, a proxy for soil pH. Our results show that the new high resolution chromatography method leads to a significant but small offset (<0.01 or <0.8°C) in TEX86, especially at low values, while no difference is observed for the CBT′. However, for the MBT5Me a significant difference is observed (<0.01 or <3°C), especially at low values, although this difference is smaller than the calibration error (4.8°C).

A new model for biomineralization and trace-element signatures of Foraminifera tests

Abstract. The Mg/Ca ratio of Foraminifera calcium carbonate tests is used as proxy for seawater temperature and widely applied to reconstruct global paleo-climatic changes. However, the mechanisms involved in the carbonate biomineralization process are poorly understood. The current paradigm holds that calcium ions for the test are supplied primarily by endocytosis of seawater. Here, we combine confocal-laser scanning-microscopy observations of a membrane-impermeable fluorescent marker in the extant benthic species Ammonia aomoriensis with dynamic 44Ca-labeling and NanoSIMS isotopic imaging of its test. We infer that Ca for the test in A. aomoriensis is supplied primarily via trans-membrane transport, but that a small component of passively transported (e.g., by endocytosis) seawater to the site of calcification plays a key role in defining the trace-element composition of the test. Our model accounts for the full range of Mg/Ca and Sr/Ca observed for benthic Foraminifera tests and predicts the effect of changing seawater Mg/Ca ratio. This places foram-based paleoclimatology into a strong conceptual framework.

The Use of Mg/Ca as a Seawater Temperature Proxy

The underlying basis for Mg/Ca paleothermometry is that the amount of magnesium in calcite precipitated from seawater is dependent on temperature. Here we review the state of the art of the Mg/Ca seawater paleotemperature proxy, summarized by the following: 1) Calcite, whether formed abiotically or biologically as foraminifera and ostracode shells, incorporates variable amounts of magnesium into the crystal structure. 2) Uptake of Mg varies positively with temperature. 3) The relationship between temperature and the amount of Mg in calcite has been quantified by experiments on synthetic calcite growth and by culture, core top, and sediment trap experiments using living organisms. 4) The most careful calibrations of the Mg/Ca paleothermometer have been done for planktic foraminifera, then benthic foraminifera; there are species-specific variations in the amount of Mg incorporated into foraminifera shells. 5) The Mg/Ca ratio of calcite from planktic foraminifera in deep-sea cores has been widely used to interpret sea surface temperatures. 6) Measurement of both Mg/Ca and δ18O in planktic foraminifera have been used to calculate δ18O in seawater, and after correction for global ice volume, salinity could be inferred. 7) Mg/Ca from benthic foraminifera have been used to reconstruct deep-sea temperatures and cooling of ~12° over the last 50 million years. 8) One problem with the Mg/Ca seawater temperature proxy is partial dissolution of foraminifer shells, which lowers the Mg/Ca, and leads to an underestimation of ocean temperature. Benthic foraminifers appear to be more resistant to partial dissolution. 9) Past changes in the Mg/Ca ratio of seawater are an important factor in determining the amount of Mg in fossil skeletal calcite, and thus add another variable to the Mg/Ca temperature proxy. All Mg/Ca paleotemperature studies on fossil calcite older than Pleistocene should take into account the Mg/Ca of the seawater from which it precipitated.

Surface and subsurface seawater temperature reconstruction using Mg/Ca microanalysis of planktonic foraminifera Globigerinoides ruber, Globigerinoides sacculifer, and Pulleniatina obliquiloculata

Laser–ablation inductively coupled plasma–mass spectrometry microanalyses of Mg/Ca across individual final chambers of three planktonic foraminifera species, Globigerinoides ruber, G. sacculifer, and Pulleniatina obliquiloculata, reveal significant interspecies differences in test Mg concentrations. Whereas these three species have similar Mg/Ca values at low sea surface temperatures (∼22°C), they diverge markedly at high sea surface temperatures (∼29°C). Explanations for these differences in species Mg/Ca values based on detailed comparison of species intratest Mg/Ca distributions suggest that compositional variability within tests cannot account for the observed deviation of species Mg/Ca values in warm‐water equatorial regions. Multiple regression modeling and δ18O analysis of Globigerinoides sacculifer tests indicate that interspecies differences in Mg/Ca values result from different depth habitats. The average Mg/Ca values of G. ruber final chambers reflect the temperature of the surface mixed layer (0–25 m), whereas those of G. sacculifer and Pulleniatina obliquiloculata correlate best with subsurface temperatures at 50–75 m and 100–125 m water depths, respectively. Mg/Ca calibration to the temperatures at these depths reveals a similar temperature control on Mg test composition in all species. Combining our results with Mg/Ca values from published culturing experiments, we derive a generalized equation for the effect of temperature and seawater salinity on foraminiferal Mg/Ca. We also show that the Mg/Ca composition of specific calcite layers within foraminiferal tests, including the low‐Mg/Ca layers of Globigerinoides ruber and G. sacculifer and the cortex layer of Pulleniatina obliquiloculata, correlates with seawater temperature and can be used as an additional proxy for seawater temperature.

Magnesium in the lattice of calcite-shelled brachiopods

Palaeoclimate information is often extracted from Rhynchonelliform brachiopod shell calcite, in particular the inner secondary layer, via the δ 18O composition, which is a proxy for seawater temperature. Compared to δ 18O, the potential for Mg/Ca ratio, as a brachiopod seawater temperature proxy, has been neglected. The use of Mg/Ca ratio as a temperature proxy assumes that, with increasing temperature, more Mg substitutes for Ca in the calcite lattice. Brachiopod shells, like all biominerals, are composites of organic and inorganic components. This raises the possibility that magnesium is hosted by the organic components. Alternatively, magnesium may be present as a separate mineral phase, rather than a true component of the calcite lattice, or incorporated into calcite in non-ideal or variable coordination. Here we use synchrotron X-ray absorption Near Edge Spectroscopy (XANES) at the Mg K-edge to determine the local environment of magnesium in two species of brachiopod with low Mg-calcite shells, Terebratulina retusa and Notosaria nigricans and one species with a high Mg-calcite shell, Novocrania anomala. XANES at the Mg K-edge of a suite of Mg-bearing standards fingerprints the local environment of magnesium in the brachiopod shell powders as well as in situ analyses. In all cases, it is evident that magnesium is not hosted by organic components but is within the inorganic component of the shell. These data support the possibility of using brachiopod Mg/Ca ratios as a temperature proxy.

High resolution distribution of magnesium and strontium and the evaluation of Mg/Ca thermometry in Recent brachiopod shells

High resolution distribution of magnesium and strontium determined by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) are presented in this study for Recent brachiopod shells. The concentration of magnesium and strontium decreases in a similar fashion from the outer to inner regions of shells of rhynchonelliform species but remains unaltered in craniid brachiopods. In rhynchonelliform brachiopods with low-magnesium shells, there is a characteristic chemical profile with an abrupt decrease in magnesium concentration from the primary layer towards the secondary layer until it reaches a region in which the values are almost constant. In addition, there is a proportional relationship in magnesium concentration between primary and secondary layers. Both findings demonstrate the biological control in magnesium incorporation in rhynchonelliform brachiopods confirming previously reported findings. Calculated Mg/Ca ratios based on magnesium concentrations within the innermost region of the secondary layer show that rhynchonelliform brachiopods can record seawater temperature. This finding opens up the possibility of using Mg/Ca (palaeo) thermometry even within the context of biological control and the potential application of Mg/Ca ratios as a seawater temperature proxy in fossil brachiopods.

Relationship between δ18O and minor element composition of Terebratalia transversa

ABSTRACTWith their extensive fossil record and shells of stable low-Mg calcite, rhynchonelliform brachiopods are attractive sources of climate information via seawater temperature proxies such as stable oxygen isotope composition. In Terebratalia transversa (Sowerby) there is a progression towards oxygen isotope equilibrium in the calcite of the innermost secondary layer. This study confirms the lack of any vital effects influencing oxygen isotope composition of T. transversa, even in specialised areas of the innermost secondary layer. Calcite Mg/Ca ratio is another potential seawater temperature proxy, that has the advantage of not being influenced by salinity. Mg concentrations measured by electron microprobe analyses indicate that there is no concomitant decrease in Mg concentration towards the inner secondary layer, associated with the progressive shift towards oxygen isotope equilibrium. Mg distribution is heterogeneous throughout the shell and correlates with that of sulphur, which may be a proxy for organic components, suggesting that some of the Mg may not be in the calcite lattice. It is essential therefore, to determine the chemical environment of the magnesium ions to avoid any erroneous temperature extrapolations in brachiopods or any other calcite biomineral.

Several centuries of variation in skeletal extension, density and calcification in massive Porites colonies from the Great Barrier Reef: A proxy for seawater temperature and a background of variability against which to identify unnatural change

Annual variations in skeletal density were measured by gamma densitometry in 35 cores removed from large Porites colonies growing at sites throughout the Great Barrier Reef (GBR). Density variations along each core provided data for average annual density and annual extension. These were used to estimate average annual calcification. Records ranged from 49 to 507 years in length. The period common to all colonies was 1934–1982. Annual growth data were averaged over periods of at least 5 years to avoid problems associated with dating of records and with measurement techniques. This also made some allowance for distortion of environmental information during coral growth and for intrusion into the environmental signal of information associated with skeletal architecture. The period common to the 10 longest cores was 1746–1982. Instrumental records of sea surface temperature (SST) are available for the GBR back to 1906. Annual calcification, averaged across these 10 cores, was significantly related to SST. Thus, average annual calcification for these 10 colonies provides a proxy for SST variations on the GBR back to the 18th century. Interpretation of evidence of a recent decline in calcification of Porites of the GBR is tempered by (1) evidence of similar declines and recoveries over the past several centuries and (2) evidence that coral calcification on the GBR has been above the long-term average for most of this century and the recent decline may be a return to more normal conditions.