Sea Surface Temperature Reconstruction Research Articles

Fossil biocalcite remains open to isotopic exchange with seawater for tens of millions of years

Fossilized remains of marine calcifiers constitute the physical basis for reconstructions of both deep ocean and sea-surface temperatures going back millions of years, but paleoclimate records derived from their isotope and trace-element chemistry can be biased by diagenesis. Experiments simulating diagenesis in the presence of an 18O-rich seawater analogue were conducted with modern and 14 Myr old foraminifera (Ammonia sp.) tests to investigate their relative susceptibility to oxygen isotope exchange. The fossilized tests were of exceptional preservation and similar to modern tests in terms of structure and crystalline organization, but had experienced partial loss of embedded organic structures, thus a priori offering fewer preferential pathways for porewaters to penetrate the tests. NanoSIMS imaging revealed that oxygen isotope exchange was pervasive in fossil tests, with isotopic exchange occurring at approximately half the rate of modern tests. The results unequivocally show that fossil biocalcites are metastable and remain more susceptible to isotope exchange than abiotic calcites millions of years after sedimentation and burial.

Tree Rings Reveal ENSO in the Last Millennium

AbstractWe present new climate field reconstructions (CFR) of tropical Pacific ENSO sea surface temperatures (HadISST) for the boreal winter season using a circum‐Pacific tree‐ring network from known El Niño rainfall impact regions. We use two different CFR methods: Point‐by‐Point Regression (PPR) and reduced‐space Orthogonal Spatial Regression (OSR). Both methods produce reconstructions with high validation skill, but OSR is preferred because it has less spatial noise and is more efficient. Only the leading EOF of the SST field (EOF1) can be skillfully reconstructed by either method; EOF2 does not validate. The success of EOF1 reflects its importance for ENSO rainfall impacts over land; the failure with EOF2 is from the lack of these impacts. EOF1 allows for the reconstruction of many ENSO indices, including the ENSO Longitudinal Index (ELI). We also find evidence in our reconstructions for a recent increase in ENSO activity.

A Comprehensive Evaluation of Machine Learning on Coral Trace Element Paleothermometers for Sea Surface Temperature Reconstruction

AbstractThis research introduces a novel approach to reconstruct sea surface temperature (SST) by developing a universal coral thermometer using machine learning (ML) algorithms on monthly resolved Porites coral proxies and SST data. A total of 1,202 data sets from 19 corals, covering SSTs ranging from 21.5 to 31.5°C, with proxies including Sr/Ca, Mg/Ca, Li/Mg, U/Ca, and B/Ca ratios were analyzed. The data were divided into four sub‐datasets by regional and taxon constraints. An exhaustive analysis was conducted, training 1,612 models using various proxy combinations and ML strategies to assess the impact of the non‐SST effect on the universality of ML models. The results indicated that the non‐SST effect is more significantly attributed to regional variations than to taxon differences, underscoring the importance of regional factors in Porites coral proxy‐based SST reconstructions. Sr/Ca and Li/Mg proxies were identified as the most indicative of SST, showing clearer relationships with temperature than other proxies. Non‐linear approaches achieved a Root Mean Square Error (RMSE) of less than 0.90°C, which further decreased to 0.72°C upon incorporating specific regional and taxon constraints. In an independent test set focusing exclusively on Li/Mg and Sr/Ca proxies, the tree‐based algorithms particularly excelled, achieving an average RMSE improvement of at least 0.52°C over the Universal Multi‐Trace Element Calibration Scheme and the Li/Mg empirical equation. This research underscores the potential of applying ML to coral‐based SST reconstructions, especially highlighting the effectiveness of tree‐based algorithms and the suitability of Sr/Ca and Li/Mg proxies for accurate temperature estimations.

High-resolution UK’37 sea surface temperature reconstruction in the southwestern Atlantic Ocean during the Holocene

Modern sea surface temperatures (SST) were assessed using the alkenone calibration index (UK′37; SST-UK′37) values from twenty-one core-top sediment samples collected along the Southwestern Atlantic Ocean and validated by comparison with satellite-derived SSTs. The SST-UK′37 values revealed an annual signal between 28 and 30°S and a winter signal (83% of the region samples) between 30 and 34° S, with deviations falling within the UK′37 calibration error range. The paleotemperature (SST-UK′37) reconstruction through the Holocene was performed using two high-resolution marine sediment cores from 33 to 34°S latitude band. Millennial-scale variations dominate most of the SST-UK′37 results with changes up to ∼6 °C. Considering the modern ocean circulation dynamics, the SST-UK’37 in our records likely stems from the combined influence of the Subtropical Shelf Front (STSF) position and the interaction between the warm, salty, and nutrient-poor Subtropical Shelf Water (STSW) and the cold, fresh, and nutrient-rich Subantarctic Shelf Water (SASW). Our SST-UK’37 results also suggest that the northernmost position limit of the STSF reached around 33°S during the mid-to-late Holocene, while after ∼5500 cal yr BP the Plata Plume Water became the dominant influence on the regional SST-UK’37 signal. Spectral analyses revealed statistically significant oscillations of ∼8600 and ∼ 2250 years in record MDBT 557, and ∼ 5300 and ∼ 2600 years in record MDBT 561 which suggests the influence of Southern Westerly Winds (SWW) on the SST-UK’37, and therefore, on the STSF dynamic through the Holocene.

Coral Sr/Ca-SST reconstruction from Fiji extending to ~1370 CE reveals insights into the Interdecadal Pacific Oscillation.

The southwestern tropical Pacific is a key center for the Interdecadal Pacific Oscillation (IPO), which regulates global climate. This study introduces a groundbreaking 627-year coral Sr/Ca sea surface temperature reconstruction from Fiji, representing the IPO's southwestern pole. Merging this record with other Fiji and central tropical Pacific records, we reconstruct the SST gradient between the southwestern and central Pacific (SWCP), providing a reliable proxy for IPO variability from 1370 to 1997. This reconstruction reveals distinct centennial-scale temperature trends and insights into Pacific-wide climate impacts and teleconnections. Notably, the 20th century conditions, marked by simultaneous basin-scale warming and weak tropical Pacific zonal-meridional gradients, deviate from trends observed during the past six centuries. Combined with model simulations, our findings reveal that a weak SWCP gradient most markedly affects IPO-related rainfall patterns in the equatorial Pacific. Persistent synchronous western and central Pacific warming rates could lead to further drying climate across the Coral Sea region, adversely affecting Pacific Island nations.

Sensitivity of Australian Rainfall to Driving SST Data Sets in a Variable‐Resolution Global Atmospheric Model

AbstractIn this study, we employ the Conformal Cubic Atmospheric Model (CCAM), a variable‐resolution global atmospheric model, driven by two distinct sea surface temperature (SST) data sets: the 0.25° Optimum Interpolation Sea Surface Temperature (CCAM_OISST) version 2.1 and the 2° Extended Reconstruction SSTs Version 5 (CCAM_ERSST5). Model performance is assessed using a benchmarking framework, revealing good agreement between both simulations and the climatological rainfall spatial pattern, seasonality, and annual trends obtained from the Australian Gridded Climate Data (AGCD). Notably, wet biases are identified in both simulations, with CCAM_OISST displaying a more pronounced bias. Furthermore, we have examined CCAM’s ability to capture El Niño‐Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) correlations with rainfall during Austral spring (SON) utilizing a novel hit rate metric. Results indicate that only CCAM_OISST successfully replicates observed SON ENSO‐ and IOD‐rainfall correlations, achieving hit rates of 86.6% and 87.5%, respectively, compared to 52.7% and 41.8% for CCAM_ERSST5. Large SST differences are found surrounding the Australian coastline between OISST and ERSST5 (termed the “Coastal Effect”). Differences can be induced by the spatial interpolation error due to the discrepancy between model and driving SST. An additional CCAM experiment, employing OISST with SST masked by ERSST5 in 5° proximity to the Australian continent, underscores the “Coastal Effect” has a significant impact on IOD‐Australian rainfall simulations. In contrast, its influence on ENSO‐Australian rainfall is limited. Therefore, simulations of IOD‐Australian rainfall teleconnection are sensitive to local SST representation along coastlines, probably dependent on the spatial resolution of driving SST.

Synthetic and practical reconstructions of SST and seawater pH using the novel multiproxy SMITE method.

Geochemical proxies of sea surface temperature (SST) and seawater pH (pHsw) in scleractinian coral skeletons are valuable tools for reconstructing tropical climate variability. However, most coral skeletal SST and pHsw proxies are univariate methods that are limited in their capacity to circumvent non-climate-related variability. Here we present a novel multivariate method for reconstructing SST and pHsw from the geochemistry of coral skeletons. Our Scleractinian Multivariate Isotope and Trace Element (SMITE) method optimizes reconstruction skill by leveraging the covariance across an array of coral elemental and isotopic data with SST and pHsw. First, using a synthetic proxy experiment, we find that SMITE SST reconstruction statistics (correlation, accuracy, and precision) are insensitive to noise and variable calibration period lengths relative to Sr/Ca. While SMITE pHsw reconstruction statistics remain relative to δ11B throughout the same synthetic experiment, the magnitude of the long-term trend in pHsw is progressively lost under conditions of moderate-to-high analytical uncertainty. Next, we apply the SMITE method to an array of seven coral-based geochemical variables (B/Ca, δ11B, Li/Ca, Mg/Ca, Sr/Ca, U/Ca & Li/Mg) measured from two Bermudan Porites astreoides corals. Despite a <3.5 year calibration period, SMITE SST and pHsw estimates exhibit significantly better accuracy, precision, and correlation with their respective climate targets than the best single- and dual-proxy estimators. Furthermore, SMITE model parameters are highly reproducible between the two coral cores, indicating great potential for fossil applications (when preservation is high). The results shown here indicate that the SMITE method can outperform the most common coral-based SST and pHsw reconstructions methods to date, particularly in datasets with a large variety of geochemical variables. We therefore provide a list of recommendations and procedures for users to begin implementing the SMITE method as well as an open-source software package to facilitate dissemination of the SMITE method.

A Daily High-Resolution Sea Surface Temperature Reconstruction Using an I-DINCAE and DNN Model Based on FY-3C Thermal Infrared Data

The sea surface temperature (SST) is one of the most important parameters that characterize the thermal state of the ocean surface, directly affecting the heat exchange between the ocean and the atmosphere, climate change, and weather generation. Generally, due to factors such as the weather, satellite scanning orbit range, and satellite sensor malfunction, there are large areas of missing satellite remote sensing SST data, greatly reducing data utilization. In this situation, how to use effective data or avenues to rebuild missing SST data has become a research hotspot in the field of ocean remote sensing. Based on the SST data from an FY-3C visible and infrared radiometer with a spatial resolution of 5 km (FY-3C VIRR), an improved data interpolation convolutional autoencoder (I-DINCAE) was used to reconstruct the missing SST data. Through cross-validation, the accuracy of the reconstruction results was quantitatively evaluated with an RMSE of 0.36 °C and an MAE of 0.24 °C. The results showed that the I-DINCAE algorithm outperformed the original DINCAE algorithm greatly. For further optimization, a deep neural network (DNN) was chosen to adjust the error between the reconstructed SST and the in situ data. The RMSE of the final adjusted SST and in situ data is 0.466 °C, and the MAE is 0.296 °C. Compared to the in situ data, the accuracy of the adjusted data has shown a significant improvement over the reconstructed data. This method successfully applies deep-learning technology to the reconstruction of SST data, achieving the full coverage and high accuracy of SST products, which can provide more reliable and complete SST data for marine scientific research.

Early to Middle Miocene Astronomically Paced Climate Dynamics in the Eastern Equatorial Atlantic

AbstractDetailed analysis of tropical climate dynamics is lacking for the Early to Middle Miocene, even though this time interval bears important analogies for future climates. Based on high‐resolution proxy reconstructions of sea surface temperature, export productivity and dust supply at Ocean Drilling Program Site 959, we investigate astronomical forcing of the West African monsoon in the eastern equatorial Atlantic across the prelude, onset, and continuation of the Miocene Climatic Optimum (MCO; 18–15 Ma). Along with previously identified eccentricity periodicities of ∼400 and ∼100 kyr, our records show that climate varied on ∼27–17 kyr, ∼41 kyr, and ∼60–50 kyr timescales, which we attribute to precession, obliquity, and their combination tones, respectively. The relative contribution of these astronomical cycles differed between proxies and through time. Three intervals with distinct variability were recognized, which are particularly clear in the temperature record: (a) strong eccentricity, obliquity, and precession variability prior to the MCO (18.2–17.7 Ma), (b) strong influence of obliquity just after the onset of the MCO (16.9–16.3 Ma) concurring with a 2.4 Myr eccentricity minimum, and (c) dominant eccentricity and precession variability during the MCO between 16.3 and 15.0 Ma. Sedimentation at Site 959 was influenced by astronomically paced variations in upwelling intensity and North African aridity related to West African monsoon dynamics. Continuously present patterns of precession imply low‐latitude forcing, while asymmetric eccentricity and obliquity imprints and strong obliquity influence suggest that Site 959 was also affected by high‐latitude, glacial‐interglacial dynamics.

Towards spatio-temporal comparison of simulated and reconstructed sea surface temperatures for the last deglaciation

Abstract. An increasing number of climate model simulations is becoming available for the transition from the Last Glacial Maximum to the Holocene. Assessing the simulations' reliability requires benchmarking against environmental proxy records. To date, no established method exists to compare these two data sources in space and time over a period with changing background conditions. Here, we develop a new algorithm to rank simulations according to their deviation from reconstructed magnitudes and temporal patterns of orbital and millennial-scale temperature variations. The use of proxy forward modeling allows for accounting for non-climatic processes that affect the temperature reconstructions. It further avoids the need to reconstruct gridded fields or regional mean temperature time series from sparse and uncertain proxy data. First, we test the reliability and robustness of our algorithm in idealized experiments with prescribed deglacial temperature histories. We quantify the influence of limited temporal resolution, chronological uncertainties, and non-climatic processes by constructing noisy pseudo-proxies. While model–data comparison results become less reliable with increasing uncertainties, we find that the algorithm discriminates well between simulations under realistic non-climatic noise levels. To obtain reliable and robust rankings, we advise spatial averaging of the results for individual proxy records. Second, we demonstrate our method by quantifying the deviations between an ensemble of transient deglacial simulations and a global compilation of sea surface temperature reconstructions. The ranking of the simulations differs substantially between the considered regions and timescales, which suggests that optimizing for agreement with the temporal patterns of a small set of proxies might be insufficient for capturing the spatial structure of the deglacial temperature variability. We attribute the diversity in the rankings to more regionally confined temperature variations in reconstructions than in simulations, which could be the result of uncertainties in boundary conditions, shortcomings in models, or regionally varying characteristics of reconstructions such as recording seasons and depths. Future work towards disentangling these potential reasons can leverage the flexible design of our algorithm and its demonstrated ability to identify varying levels of model–data agreement. Additionally, the algorithm can be applied to variables like oxygen isotopes and climate transitions such as the penultimate deglaciation and the last glacial inception.

Assessment of Porites microatolls for paleothermometry: Calibration for French Polynesia

Massive dome-shaped coral Porites are the predominant choice for paleoclimate studies due to their consistent and reliable growth. When growing close to sea level, they become limited in their vertical growth and form so-called ‘microatolls’. Microatolls have not yet been extensively explored for paleoclimate reconstruction. Here, we investigate how reliable modern Porites microatolls are against empirical sea-surface temperature using Sr/Ca, δ18O, Li/Mg and SrU paleothermometry methods on samples from the Society Islands, French Polynesia. Our results show Sr/Ca ratios have the lowest Standard Error of the Inverse Prediction (SEIP) at 0.415 °C (N = 41) with a calibration of Sr/Ca (mmol mol−1) = −0.082 ± 0.006 SST (°C) + 11.256 ± 0.170 and with high reproducibility across multiple corals. The reproducibility of δ18O was less good, with SEIP increasing to 0.829 °C (N = 41). Considering methods directly from the literature, Li/Mg ratio empirically corrected for Sr/Ca had the best balance between bias and precision where no local calibration could be available. This study independently evaluates and confirms the suitability of Porites microatolls from well-flushed environments for paleoclimate studies. Fossil dome-shaped Porites grow anywhere between near-surface and roughly 20 m depths which inherently incorporates uncertainty into any sea surface temperature reconstruction. This uncertainty is significantly reduced for microatolls due to their well-constrained bathymetry. The study represents a fundamental step in paleoclimate research targeting consistently near the water-air interface bringing reliability and, especially when combined with their ability to reconstruct past sea-level changes, microatolls have the potential to be central for future paleoenvironmental studies.

North Atlantic Temperature Change Across the Eocene‐Oligocene Transition From Clumped Isotopes

AbstractThe Eocene‐Oligocene transition (EOT) (∼34 Ma) is marked by the rapid development of a semi‐permanent Antarctic ice‐sheet, as indicated by ice‐rafted debris and a 1–1.5‰ increase in deep sea δ18O. Proxy reconstructions indicate a drop in atmospheric CO2 and global cooling. How these changes affected surface ocean temperatures in the North Atlantic and ocean water stratification remains poorly constrained. In this study, we apply clumped‐isotope thermometry to well‐preserved planktonic foraminifera, that are associated with lower mixed‐layer to subthermocline dwelling depths from the drift sediments at international ocean discovery program Site 1411, Newfoundland, across four intervals bracketing the EOT. The thermocline/lower mixed‐layer dwelling foraminifera record a cooling of 1.9 ± 3.5 K (mean ± 95% CI) across the EOT. While the cooling amplitude is similar to previous sea surface temperature (SST) reconstructions, absolute temperatures (Eocene 20.0 ± 2.9°C, Oligocene 18.0 ± 2.2°C) appear colder than previous organic proxy reconstructions for the northernmost Atlantic extrapolated to this location. We discuss seasonal bias, recording depth, and appropriate consideration of paleolatitudes, all of which complicate the comparison between SST reconstructions and model output. Our subthermocline dwelling foraminifera record a larger cooling across the EOT (Eocene 19.0 ± 3.5°C, Oligocene 13.0 ± 3.2°C, cooling of 5.5 ± 4.6 K) than foraminifera from the thermocline/lower mixed‐layer, consistent with global cooling and an increase in ocean stratification which may be related to the onset or intensification of the Atlantic meridional overturning circulation.

Reconstructed seasonality during the Mid Piacenzian Warm Interval and early Pleistocene cooling as recorded by growth temperatures from Mercenaria shells

The Mid Piacenzian Warm Interval (MPWI) has been identified as an analogue for future global warming because it had warmer temperatures and higher atmospheric CO2 levels than today, while subsequent early Pleistocene cooling is more similar to modern climate. However, reconstructions of these intervals lack seasonal-scale temperature reconstructions. Seasonal sea surface temperature (SST) reconstructions from deep-time archives can potentially provide insight into the nature of the climate system on sub-annual scales during critical climate states. Here we compared seasonal variability in growth temperatures during the MPWI and subsequent early Pleistocene cooling to modern climate reconstructed from oxygen isotope ratios recorded by the bivalve Mercenaria. Modern shells were collected from the University of North Carolina's Marine Sanctuary. Fossil shells from the Mid-Atlantic Coastal Plain (North Carolina) were collected from the Duplin Formation (MPWI) and the Waccamaw Formation (early Pleistocene). Oxygen isotope ratios range from −1 to 2.4 ‰ during the MPWI, −1–2.4 ‰ during the early Pleistocene, and −2.2 to 2.3 ‰ in modern shells. Stable carbon isotope ratios ranged from −0.91 to 1.67 ‰ during the MPWI, 0.19–1.87 ‰ during the early Pleistocene, and −2.46 to 0.60 ‰ in modern shells. Average seasonal growth temperature variations for the MPWI (∼11 ± 3 °C) are reduced compared to modern instrument records (∼16 ± 3 °C), while the early Pleistocene (∼14 ± 2 °C) was more similar to today. Modern Mercenaria record dark increment formation during the summer while fossil Mercenaria record dark increment formation during the winter. We hypothesize that this difference is timing of dark increment formation may be due in part to differences in water depth (∼1m for modern shells and ∼20m for fossil shells) or a shift in the location of the boundary between biogeographic zones. A −1.6 ‰ shift in mean stable carbon isotope ratios between fossil (0.92 ± 0.66 ‰) and modern (−0.65 ± 0.44 ‰) shells has been observed and may be a result of the “Suess Effect” and/or influences of estuarine/freshwater relative to marine settings.

20th Century Warming in the Western Florida Keys Was Dominated by Increasing Winter Temperatures

AbstractLong‐lived Atlantic coral species like Orbicella faveolata are important archives of oceanographic change in shallow, marine environments like the Florida Keys. Not only can coral‐based records extend for multiple centuries beyond the limits of the instrumental record, but they can also provide a more accurate representation of in situ conditions than gridded interpolated sea‐surface temperature (SST) products for nearshore reef environments. We use the coral Sr/Ca paleothermometer to produce a 150‐year (1830–1980 C.E.) monthly SST reconstruction from an O. faveolata colony collected in the Marquesas Keys, FL, USA. An important feature of our record is a significant 20th‐century warming trend in winter SSTs. We hypothesize that the winter warming trend was driven partially by a decrease in upwelling associated cyclonic eddies spinning off the Florida Current. A long‐term weakening of winter Florida Current transport over the 20th century could be responsible for decreased cyclonic eddy formation in the Florida Straits. Another feature of the record is pronounced multidecadal fluctuations of mean annual warming and cooling in the record, which correspond to Atlantic Multidecadal Variability (AMV), with the AMV lagging behind western Florida Keys temperatures by 5–11 years. Strong coherence between coral‐based SST reconstructions in the western Florida Keys with broader scale Atlantic oceanographic trends over the past century suggests a common driver of regional SST variability.

Sea surface temperature reconstruction in the Pacific Ocean using multi-elemental proxy in Porites and Diploastrea corals: Application to Palau Archipelago

Massive reef-building Porites corals are commonly studied to obtain long-term reconstructions of past sea surface temperature (SST) using temperature-sensitive elemental proxies, such as Sr/Ca or Li/Mg ratios. Most recently, a multi-proxy approach combining these two ratios (e.g. D'Olivo et al., 2018) and the SrU method (DeCarlo et al., 2016) have proved to be more robust to reconstruct paleo-temperatures. To date, no study has been carried out on the application of these new approaches on the Diploastrea heliopora coral, another massive reef-building genus that can potentially provide longer temperature records. Moreover, only a few studies have assessed coral SST calibrations at the scale of the Indo-Pacific basin and compared SST reconstructions obtained from two massive coral genera from the same site.In this study, we investigated the elemental composition of the topmost portion of 34 modern tropical Porites and 6 Diploastrea colonies collected during the Tara Pacific expedition (2016–2018) from various hydrological contexts in the Pacific Ocean. We derived and discussed annual Sr/Ca, Li/Mg, combined Sr/Ca-Li/Mg and Sr/Ca-Li/Ca-Mg/Ca and SrU vs. SST calibrations as well as potential intra-colonial and genus specific effects and evaluated the use of these basin-wide calibration equations. Overall, multi-ratio and multi-genera SST calibrations perform better than single-ratio calibrations and seem to improve temperature reconstructions.These new SST calibrations were applied to two colonies of Porites and Diploastrea collected from the same site in the North-West of the Palau archipelago located in the western Pacific Ocean to evaluate the applicability of universal calibrations based on different proxies and their combination. Coral-based SST records spanning the last 141 years show decadal changes and recent warming episodes that are related to major El Niño Southern Oscillation events. However, differences in reconstruction remain between both genera in the long-term trends, amplitudes, and absolute temperatures, depending on which genus or temperature proxy is considered.

Major Diatom Microfossils from the Arctic Region: A Review

Abstract Diatoms-the unicellular, eukaryotic, photosynthetic phytoplankton belonging to Class Bacillariophyceae are an excellent tool to understand past ocean surface conditions, especially in high latitude regions. Along with sea surface temperature and sea ice, which they are primarily sensitive to, diatom assemblages could potentially be used to record runoff from melting glaciers and atmospheric teleconnections such as North Atlantic Oscillations (NAO) in Arctic fjords. However, understanding the ecology and geographical distribution of diatoms is extremely important before they can be used for palaeoceanographic reconstructions. In this study, four significant Arctic diatoms namely Bacterosira bathyomphala, Fragilariopsis cylindrus, Fragilaripsis oceanica and Thalassiosira antarctica var. borealis resting spores (R.S.) have been reviewed to understand their current status in their use for palaeoceanographic reconstructions. These four diatoms have been selected as they represent a typical Arctic environment. Numerous studies in the past thirty years had classified these diatoms into different assemblage groups, indicating specific ocean surface conditions. Here, we review the previous studies and to present the up-to-date classification of these species. We also compared the change in abundance of these four species through mid to late Holocene and modern period to their respective sea surface temperature and sea ice reconstructions, to show the robustness of their usage in palaeoceanographic reconstructions. The findings of this study will help to understand the up-to-date ecological characteristics of Arctic diatoms used in palaeoceanographic as well as palaeoecological reconstructions and the gap areas in diatom research such as a requirement for pan Arctic Sea ice diatom dataset.

Weathering pulses during glacial-interglacial transitions: Insights from well-dated paleosols in the Azores volcanic province (Central North Atlantic)

Volcanic islands evolve through complex interactions between volcano growth and surface processes. Climate changes impact the physical and chemical processes that drive weathering and denudation. While global paleoclimate has been extensively studied for the late Quaternary, elucidating the local climatic response to global forcing on such islands remains challenging. São Miguel is a volcanic island in the Eastern Azores, located in the Central North Atlantic, a region susceptible to changes in large-scale atmospheric and oceanic dynamics. It comprises numerous paleosols (PSs), whose geochemistry results from volcanic rocks' weathering and can serve as a proxy to reconstruct paleoclimatic conditions. New K–Ar and 40Ar/39Ar ages of volcanic units “bracketing” (under and overlying) PSs reveal four periods of enhanced soil formation (∼820–765 ka, ∼425–430 ka, ∼170–75 ka, <10 ka), coinciding with rapid glacial-interglacial transitions (Terminations I, II, V, IX). Our reconstructed mean annual precipitation (MAP; 500–1200 mm yr−1) and air temperature (MAAT; 12–18 °C) are higher during interglacial peaks. This, in addition to the coherence of MAAT with previous Sea Surface Temperature reconstructions, shows consistency between local and global climate dynamics. The texture of parental rocks played a significant role in weathering, with PSs predominantly restricted to the brecciated upper part of lava flows and to pyroclastic deposits, which exhibited distinctive precipitation thresholds for their formation (∼800 mm yr−1 and ∼500 mm yr−1, respectively). PSs developed on basaltic lava flows exhibit greater elemental loss, due to a high glass proportion and low permeability, which prevents fluids percolation out of the soils. As present-day precipitation and temperature exceed those of the past, enhanced weathering is expected in São Miguel and other volcanic islands, with local to global impacts (e.g., carbon cycling), especially in the context of ongoing global warming.

NORWEGIAN SEA HOLOCENE ENVIRONMENTS BASED ON THE FOSSIL MICROALGAE ASSEMBLAGES

Detailed micropaleontological analysis was performed on the sediment core AMK-6142 collected in the deep-sea southwestern part of the Lofoten Basin in the Norwegian Sea. Summer sea-surface temperature for the last 7 cal. ky was reconstructed from dinocyst assemblages using the modern analogue technique (MAT). Sea-surface temperature reconstruction and dinocysts species composition indicate repeated changes in the surface environments during the Middle and Late Holocene. Episodes of cooling and probable displacement of the Arctic Front to the southwestern part of the Lofoten Basin were recorded for 5–7, 1.6–2.1, and 0.1–1.0 cal. ka BP.

Super Resolution of Satellite-Derived Sea Surface Temperature Using a Transformer-Based Model

Sea surface temperature (SST) is one of the most important factors related to the ocean and the climate. In studying the domains of eddies, fronts, and current systems, high-resolution SST data are required. However, the passive microwave radiometer achieves a higher spatial coverage but lower resolution, while the thermal infrared radiometer has a lower spatial coverage but higher resolution. In this paper, in order to improve the performance of the super-resolution SST images derived from microwave SST data, we propose a transformer-based SST reconstruction model comprising the transformer block and the residual block, rather than purely convolutional approaches. The outputs of the transformer model are then compared with those of the other three deep learning super-resolution models, and the transformer model obtains lower root-mean-squared error (RMSE), mean bias (Bias), and robust standard deviation (RSD) values than the other three models, as well as higher entropy and definition, making it the better performing model of all those compared.

Caribbean salinity anomalies contributed to variable North Atlantic circulation and climate during the Common Era.

Paleoceanographic reconstructions show that the strength of North Atlantic currents decreased during the Little Ice Age. In contrast, the role of ocean circulation in climate regulation during earlier historical epochs of the Common Era (C.E.) remains unclear. Here, we reconstruct sea surface temperature (SST) and salinity in the Caribbean Basin for the past 1700 years using the isotopic and elemental composition of planktic foraminifera tests. Centennial-scale SST and salinity variations in the Caribbean co-occur with (hydro)climate changes in the Northern Hemisphere and are linked to a North Atlantic SST forcing. Cold phases around 600, 800, and 1400 to 1600 C.E. are characterized by Caribbean salinification and Gulf of Mexico freshening that implies reductions in the strength of North Atlantic surface circulation. We suggest that the associated changes in the meridional salt advection contributed to the historical climate variability of the C.E.