Surface Water Temperature Variations Research Articles

Investigating the Morphometry and Hydrometeorological Variability of a Fragile Tropical Karstic Lake of the Yucatán Peninsula: Bacalar Lagoon

Comprehensive morphometric and hydrometeorological studies on Bacalar Lagoon, Mexico’s largest tropical karstic lake and a significant aquatic system of the Yucatán Peninsula, are lacking. This study provides a detailed analysis of its bathymetry, morphometry, and hydrometeorological characteristics. The lake’s main basin stretches more than 52.7 km in length, with widths varying from 0.18 km to 2.28 km. It has a volume of 554.4 million cubic meters, with an average depth of 8.85 m, reaching depths of up to 26 m in the north and featuring sub-lacustrine dolines in the south, with depths of 38 m, 48.5 m, and 63.6 m. The study reveals seasonal variations in surface water temperature, closely linked to air temperature (r = 0.89), and immediate responses of water levels to hydrometeorological events. Water level fluctuations also exhibit seasonal patterns that are correlated with regional aquifer conditions, with a lag of 2 months after seasonal rainfall. Interannual variability in rainfall and water levels was observed. From 2010 to 2012, rainfall consistently remained below its mean climatic value, due to a prolonged La Niña event, while the exceptionally wet conditions in 2020 were also associated with La Niña. Extreme and anomalous hydrometeorological events, such as those following tropical storm Cristobal in 2020, revealed the fragility of Bacalar Lagoon, causing a notable transformation in lake color and transparency, shifting it from its typical oligotrophic state to eutrophic conditions that lasted longer than a year. These color changes raise questions about the factors impacting ecological health in tropical karstic regions. Additional factors affecting water quality in the BL in 2020, such as deforestation, coastline changes, and urban growth, warrant further investigation. Our study can serve as a starting landmark.

The impact of extreme heat on lake warming in China

Global lake ecosystems are subjected to an increased occurrence of heat extremes, yet their impact on lake warming remains poorly understood. In this study, we employed a hybrid physically-based/statistical model to assess the contribution of heat extremes to variations in surface water temperature of 2260 lakes in China from 1985 to 2022. Our study indicates that heat extremes are increasing at a rate of about 2.08 days/decade and an intensity of about 0.03 °C/ day·decade in China. The warming rate of lake surface water temperature decreases from 0.16 °C/decade to 0.13 °C/decade after removing heat extremes. Heat extremes exert a considerable influence on long-term lake surface temperature changes, contributing 36.5% of the warming trends within the studied lakes. Given the important influence of heat extremes on the mean warming of lake surface waters, it is imperative that they are adequately accounted for in climate impact studies.

Detection of surface water temperature variations of Mongolian lakes benefiting from the spatially and temporally gap-filled MODIS data

• We applied an effective spatiotemporal gap-filled method to improve the LSWT from MODIS. • The long-term variations of the annual and seasonal mean LSWTs of Mongolian lakes were provided. • The LSWT of Mongolian lakes confirmed the phenomenon “global warming hiatus”. Lakes provide critical water resources for human activities and ecosystems, particularly in the Mongolian Plateau (MP), which is characterized by a dry climate and a harsh environment. As a region that is sensitive to anthropogenic warming, tracking lake surface water temperature (LSWT) changes in Mongolian lakes is crucial for understanding the consequences of a warming climate on lake ecosystems. However, the long-term monitoring of LSWT is restricted by the spatiotemporal gaps in the raw imagery of remote sensing-based land surface temperature (LST), e.g., the commonly used Moderate Resolution Imaging Spectroradiometer (MODIS) LST products. This study applied an improved gap-filling method by utilizing the discrete cosine transform-based penalized least squares (DCT-PLS) strategy in the spatial domain combined with the linear interpolation (LI) algorithm in the temporal domain. The method was applied to fill gaps in the LSWT imagery of 12 representative lakes across MP. The randomly sampled high-quality MODIS LSWT values in the spatial and temporal domains were excavated as false data gaps and considered “virtual true” validation datasets. The spatial validation results showed that the estimated LSWT for all the lake cases were comparable with the “virtual true” LSWT values, with the average values of the coefficient of determination, mean absolute error, mean square error, and root mean square error being 0.98, 0.38 °C, 0.45 °C, and 0.59 °C, respectively. Meanwhile, the error of nighttime LSWT results was relatively lower than that of daytime LSWT. For temporal interpolation validation, the LI algorithm exhibited relatively better performance and could more objectively indicate the variation in LSWT. Benefiting from the spatially and temporally well-constrained data, we analyzed the interannual and intra-annual change characteristics of the LSWTs of the 12 lakes. The long-term variations of annual and seasonal mean LSWTs in the 12 selected lakes exhibited no evident trends in 2000–2020, while presented apparent interannual fluctuations. The slight changes in the average LSWTs of the 12 selected lakes were in excellent synchronization with the surrounding LST derived from the reanalysis datasets, confirming the widely reported phenomenon of “global warming hiatus” that occurred in the early 21st century. This study improves the understanding of the LSWT variations in Mongolian lakes in response to global climate change. It has the potential to provide an effective approach for monitoring LSWT changes in other large-scale studies.

Determination of Marine Biotoxins Contamination Level of Mussel (Perna Perna) (Linne, 1758) from the Mamelles Bay, Dakar

This study evaluating marine biotoxins contamination level of mussel ( Perna Perna ) in the Mamelles Bay (Ouakam) of Dakar is the first report in Senegal. It took place over one year (from March 2018 to February 2019). Liquid chromatography with mass spectrometry (LC-MS-MS) reference method (Regulation (EC) 15/2011 of 10 January 2011) was used to quantify marine biotoxins. Okadaic acid (OA) and its esters are the most problematic of all the researched biotoxins. They are present throughout most of the year, except September and November, with an average monthly concentration of 163 µg/kg, slightly above the regulatory limit (160 µg/kg). The sanitary status of the mussel shows two peaks of contamination, the first of which occurs in the rainy season (August) and the second in the cold season (December), with values equal to 654 and 802 µg/kg respectively 4 to 5 times higher than the regulatory threshold set by Regulation (EC) No 853/2004 of 29 April 2004 supplemented by Regulation (EU) No 786/2013 amending its Annex III and Senegalese Order No 07951 of 12 May 2017. These two peaks coincide with (i) the wintering period, marked by continental land-based inputs due to rainwater runoff, but also with the temperature rise, or (ii) the cold period with the appearance of upwelling (upwelling of cold water, rich in nutrient salts). In addition to the chemical analyses carried out on the mussel, the research work on phytoplankton and the surveys of physicochemical parameters carried out on the water at the collection site show (i) the existence of toxic algae of the Dinophysis genus and Gambierdiscus , in June, i.e., one to two months before the first peak of contamination of the Perna perna by AO; (ii) also a coincidence between the appearance of these phenomena and variations in surface water temperature and salinity, which are determining factors in the appearance and development of harmful algal blooms. Concerning the other biotoxins investigated, in particular AZA and yessotoxins, it was noted that AZA was absent throughout the year, unlike yessotoxins, which were found in the flesh of Perna perna at concentrations below the regulatory limit set at 3750 µg/kg. The maximum being 51 µg/kg obtained in June, i.e., 73 times lower than the regulatory threshold. In the light of the results obtained, it appears that the periods of high contamination are the winter period and the upwelling period, which could lead to closure measures to guarantee the safety of the mussels. It would be interesting to extend the study to all other bivalve mollusks and gastropods, to carry out an inventory and quantify the toxic microalgae present in the water. To this end, the effectiveness of purification techniques would be tested. Keywords: Mussel ( Perna perna ), Marine biotoxins, Toxic microalgae, Mamelles, Dakar. DOI: 10.7176/FSQM/117-04 Publication date: July 31 st 2022

Surface water isoscapes (δ18O and δ2H) reveal dual effects of damming and drought on the Yangtze River water cycles

The water regimes and biogeochemical cycles are remarkably affected by river damming and drought around the world. However, the dual effects on river water cycles have not yet attracted sufficient attention along the Yangtze River because of the relative consistency of annual water regimes. This study first explored the altered water cycle associated with damming and drought using surface water isoscapes (δ18O and δ2H) of river and lake water along the Yangtze River during the flooding seasons of 2016 and 2018, combined with other historical isotopic data from 2003 to 2013. The results show that river water isotopes are markedly varied on both spatial and temporal scales. The relatively more enriched river water representing δ18O values were observed from 2003 to 2007 compared with those in 2018, which were possibly caused by increased evaporative fractionation under abnormal drought conditions in the Yangtze River. Spatially, river water δ18O values exhibited a positive trend from upstream to the lower reaches because of the contrasting recharged sources, complex mixing, and evaporation from upstream to the lower reaches of the Yangtze River. This trend was related to variations in surface water temperature and water evaporation during the flooding seasons evidenced by a significant correlation between river isotopes and river water temperature. Moreover, the large variability in deuterium-excess (d-excess) and δ18O in the downstream could be inherited from the upstream because of short residence time and incomplete mixing in the Three Gorges Reservoir (TGR) during the initial stage of the Three Gorges Dam (TGD) operation (2003–2007). In contrast, the relatively lower variability of d-excess and δ18O was found in the downstream area due to the complete mixing in the TGR, causing the homogenization of reservoir water during the normal operation stage after 2010 (e.g., 2013 and 2018). Drought stimulates evaporative fractionation on river water and result in more negative d-excess values especially in 2006. The dual effects of river damming and drought remarkably changed the longitudinal hydrological connectivity and water cycle dynamics by prolonging the residence time and enhancing the water mixing, which should be thoroughly considered for water resource management, especially for regions with heavily-regulated rivers.

Spatial and seasonal variations in surface water temperature and salinity in the Mexico‐Belize riverine estuary: Possible comfort conditions for manatees?

AbstractThe Mexican Caribbean and Belize are home to one of the largest populations of Caribbean manatees (Trichechus manatus manatus). However, the transboundary Hondo River estuary is less examined compared to the surrounding protected areas. This paper provides a quantitative description of the spatial and temporal variability in abiotic factors and manatee distribution throughout the Hondo River estuary, with monthly field measurements during 2018–2019. Simultaneously, visual observations and side‐scan sonar detection were implemented, with 84 manatee sightings reported (calves 11.9%, noncalves 88.1%). Heatmap and frequency analyses showed that most manatee sightings occurred at the riverine estuary limit, the confluences between the river and the bay into which it flows. The surface water temperature and salinity ranged 28°C ≤ T ≤ 32°C and 0.5 PSU ≤ S ≤ 4.5 PSU for ~72% of the manatees identified, potentially describing locally preferred conditions for manatees. During the regional mid‐summer drought, higher temperature (31.5°C), salinity (18 PSU), and estuary extent (17.6 km) were recorded, including the maximum peak of manatee sightings (~31%). The roles of these abiotic factors are discussed as tentative environmental comfort conditions for manatees that could reduce their energy and maintenance costs. The identification of preferred conditions could broaden perspectives on how manatees interact with their habitats.

A heterocyte glycolipid-based calibration to reconstruct past continental climate change

Understanding Earth’s response to climate forcing in the geological past is essential to reliably predict future climate change. The reconstruction of continental climates, however, is hampered by the scarcity of universally applicable temperature proxies. Here, we show that heterocyte glycolipids (HGs) of diazotrophic heterocytous cyanobacteria occur ubiquitously in equatorial East African lakes as well as polar to tropical freshwater environments. The relative abundance of HG26 diols and keto-ols, quantified by the heterocyte diol index (HDI26), is significantly correlated with surface water temperature (SWT). The first application of the HDI26 to a ~37,000 year-long sediment record from Lake Tanganyika provides evidence for a ~4.1 °C warming in tropical East Africa from the last glacial to the beginning of the industrial period. Given the worldwide distribution of HGs in lake sediments, the HDI26 may allow reconstructing SWT variations in polar to tropical freshwater environments and thereby quantifying past continental climate change.

Surface Water Temperature Predictions at a Mid-Latitude Reservoir under Long-Term Climate Change Impacts Using a Deep Neural Network Coupled with a Transfer Learning Approach

Long-term climate change may strongly affect the aquatic environment in mid-latitude water resources. In particular, it can be demonstrated that temporal variations in surface water temperature in a reservoir have strong responses to air temperature. We adopted deep neural networks (DNNs) to understand the long-term relationships between air temperature and surface water temperature, because DNNs can easily deal with nonlinear data, including uncertainties, that are obtained in complicated climate and aquatic systems. In general, DNNs cannot appropriately predict unexperienced data (i.e., out-of-range training data), such as future water temperature. To improve this limitation, our idea is to introduce a transfer learning (TL) approach. The observed data were used to train a DNN-based model. Continuous data (i.e., air temperature) ranging over 150 years to pre-training to climate change, which were obtained from climate models and include a downscaling model, were used to predict past and future surface water temperatures in the reservoir. The results showed that the DNN-based model with the TL approach was able to approximately predict based on the difference between past and future air temperatures. The model suggested that the occurrences in the highest water temperature increased, and the occurrences in the lowest water temperature decreased in the future predictions.

The changes in physicochemical and stable isotope compositions in the lower Yellow River of China due to artificial flooding

Increasingly, modern hydrological technologies are dynamically altering river water flow and drastically affecting river hydrogeochemical cycle regimes globally. The present study focused on the reservoir discharges of artificial floodwaters that influence spatiotemporal variations in the physicochemical and stable isotope compositions in the lower Yellow River (LYR) of China. The surface water samples were collected at the nine sites along the LYR during the pre-, inter-and post-flood periods. Then, the collected samples were analysed with the following standard method. The δD and δ18O slopes of the waterline clearly indicated that the prolonged reservoir water and different water flows impacted the hydrological cycle in the LYR regions compared to GMWL (global meteoric water line) and LMWL (local meteoric water line). The thermal stratification processes of the water in the largest reservoir slightly enriched the heavy isotopes, and physicochemical alteration was neglected. Statistical analysis of two-way ANOVA revealed that the p-values (p < 0.01, p < 0.05) were very strong for most of the variables between the periods, and the linear regression exhibited weak values (R2 = 0.253, R2 = 0.150) at the surface water temperature variations and suggested no significant influence of isotope composition. Overall, the Xiaolangdi reservoir water prolonged time rates, and artificial floodwater flow had a very small effect on the isotope composition; in particular, a large high turbidity concentration in the discharged artificial floodwaters was the only considerable ecological risk condition in the LYR. This kind of proper monitoring work is immensely important and prevents reservoirs from causing hydrological cycle impacts in the LYR and the adjacent coastal ecosystems.

High- and low-latitude forcing on the south Yellow Sea surface water temperature variations during the Holocene

Abstract Sea surface temperature (SST) of the modern Yellow Sea (YS) is sensitive to forcing by both the East Asian monsoon and the North Pacific western boundary current, however, detailed mechanisms for explaining the Holocene SST evolution remains to be understood. Here we present two decadal sampling resolution alkenone SST records from the south YS spanning the last 8.9 kyr to understand forcing mechanisms on different timescales. The results show that the two sites from the south YS experienced SST variations on millennial timescale, displaying mean high values of 16.5 °C (A03-B) and 15.2 °C (YS01) from 7.7 to 5.9 ka, followed by low values of 16.4 °C (A03-B) and 14.8 °C (YS01) from 5.9 to 2.9 ka, then by high values of 16.9 °C (A03-B) and 15.5 °C (YS01) from 2.9 to 0.6 ka. After the entrance of the YS Warm Current at about 7.5 ka, evolution of the south YS SSTs paralleled the pattern of the main Kuroshio Current intensity, i.e., low (high) SST coeval with weak (strong) Kuroshio Current, suggesting that millennial-scale SST variations in the south YS were primarily controlled by the Kuroshio Current. Superimposing on the millennial variations, seven abrupt centennial-scale cold events were observed during the Holocene, with SST oscillations broadly coeval with those of North Atlantic ice-rafted detritus and East Asian winter monsoon rather than SSTs from the Okinawa Tough and Indo-Pacific warm pool. Hence, we propose that the East Asian winter monsoon was the top-down conveyor transmitting North Atlantic cooling signals to the south YS on centennial timescale. Thus, our study reveals both high- and low-latitude climate forcing on the evolution of the south YS SST during the Holocene, with low-latitude forcing on millennial-scale and high-latitude forcing on centennial-scale.

Sea surface water variability during the Mid-Brunhes inferred from calcareous plankton in the western Mediterranean (ODP Site 975)

Planktonic foraminifera and calcareous nannoplankton were analyzed in core Ocean Drilling Program Site 975, located in the western Mediterranean, in order to study their response to environmental changes across the Mid-Brunhes interval and specifically through Marine Isotope Stage (MIS) 15 and 8 (ca. 650–230ka). Multivariate analysis of assemblage composition revealed that the calcareous plankton dynamics were mainly driven by surface water temperatures both on glacial-interglacial and stadial-interstadial time scales. Throughout the studied interval, foraminiferal and nannoplankton assemblages responded to environmental forcing in concert, except during MIS 15, when multiple environmental factors appear to have been superimposed on the otherwise dominating effect of temperature variability. Sea surface temperature (SST) has been estimated from planktonic foraminiferal assemblages using the artificial neural networks method pointing out relevant seasonal variations through the record. Our reconstructions reveal that calcareous plankton assemblages also responded to other environmental factors than temperature, including modification in surface water stratification, nutrient availability and detrital input. Specifically, a more stable, stratified water column seems to have accompanied the interval through MIS 15–13. On the other hand, across the Mid-Brunhes interval, from MIS 12 onwards, the enhanced glacial strength affected both planktonic foraminifera and calcareous nannofossils: planktonic foraminifera indicate that mixed and productive surface waters developed during glacials and stadials, accompanied by episodes of increased detrital input as suggested by calcareous nannoplankton assemblages. Enhanced food availability was likely driven by wind-induced upwelling and/or by continental coastal input during dry conditions persisting in the Mediterranean region and over North Africa. Finally, spectral and wavelet analyses of calcareous plankton time series allowed to identify the pattern of periodic response of the plankton at Milankovitch cycles and, in some cases, at millennial variability. The dominant 100kyr periodicity recorded in surface water temperature proxies clearly reflects a major response of the planktonic community to the global glacial-interglacial climate pattern. High-frequency variation (~5–8, ~11–13ky) of surface water temperature proxies and of selected taxa abundance highlights the occurrence of millennial-scale instability superimposed on the paleoenvironmental modifications occurring through the Mid-Brunhes interval climate transition. This framework accounts for the occurrence of different surface water dynamics across the Mid-Brunhes interval and is in favor of the hypothesis that the millennial scale surface water temperature variations are modulated by the harmonics of the precession forcing.

Spatial heterogeneity in geothermally-influenced lakes derived from atmospherically corrected Landsat thermal imagery and three-dimensional hydrodynamic modelling

Atmospheric correction of Landsat 7 thermal data was carried out for the purpose of retrieval of lake skin water temperature in Rotorua lakes, and Lake Taupo, North Island, New Zealand. The effect of the atmosphere was modelled using four sources of atmospheric profile data as input to the MODerate resolution atmospheric TRANsmission (MODTRAN) radiative transfer model. The retrieved skin water temperatures were validated using a high-frequency temperature sensor deployed from a monitoring buoy at the water surface of Lake Rotorua. The most accurate atmospheric correction method was with Moderate Resolution Imaging Spectroradiometer (MODIS) atmospheric profile data (root-mean-square-error, RMSE, 0.48K), followed by radiosonde (0.52K), Atmospheric Infrared Sounder (AIRS) Level 3 (0.54K), and the NASA atmospheric correction parameter calculator (0.94K). Retrieved water temperature was used for assessing spatial heterogeneity and accuracy of surface water temperature simulated with a three-dimensional (3-D) hydrodynamic model of Lake Rotoehu, located approximately 20km east of Lake Rotorua. This comparison indicated that the model was suitable for reproducing the dominant horizontal variations in surface water temperature in the lake. This study demonstrated the potential of accurate satellite-based thermal monitoring to validate temperature outputs from 3-D hydrodynamic model simulations. It also provided atmospheric correction options for local and global applications of Landsat thermal data.

Late-Holocene diatom-inferred reconstruction of temperature variations of the West Greenland Current from Disko Bugt, central West Greenland

The diatom flora from a high-resolution core collected from Disko Bugt, central West Greenland, records variations in surface water temperature for the late Holocene (1600—300 cal. BP). Our data support the existence of a previously identified anti-phase relationship between the surface water temperature from West Greenland and climate events recorded in the NE Atlantic and between surface and subsurface waters (identified from benthic foraminifera) of the West Greenland Current (WGC). The diatom flora record relatively cool surface water conditions during the end of the ‘Roman Warm Period’ and ‘Medieval Warm Period’ (MWP), and relatively warmer surface water conditions during the ‘Dark Ages Cold Period’ and ‘Little Ice Age’ (LIA). This is particularly pronounced during the MWP, experiencing the coldest conditions, and the LIA experiencing the warmest conditions through the whole sequence studied. The most likely explanation for this anti-phase relationship is linked to the flux of meltwater delivered to the WGC from sea ice and the Greenland ice sheet off the West Greenland margin. The generally warmer conditions of the MWP resulted in increased melting of sea ice and the Greenland ice sheet producing an increased meltwater flux and cooling of the surface waters of the WGC. In contrast, reduced meltwater flux during the relatively cold LIA resulted in reduced meltwater flux to the WGC, producing a relative warming of the surface waters recorded by the diatom flora.

MODIS-derived surface temperature of the Great Salt Lake

The surface temperature of Utah's hypersaline Great Salt Lake is examined between 2000 and 2007 using 3345 images from the Moderate Resolution Imaging Spectroradiometer (MODIS) on board the NASA Earth Observing System Terra and Aqua platforms. This study shows the utility of using a multi-year record of the easily accessible and fully processed MODIS thermal imagery to monitor spatial, diurnal, seasonal, and annual variations in the surface water temperature (SWT) of lakes where long-term in situ measurements are rarely available. A cloud-free Terra image is available on average every day during the summer and early fall, every other day during spring and late fall, and every third day during the winter. MODIS-derived lake SWT exhibits a cool bias (~ − 1.5 °C) relative to in situ temperature observations gathered from three buoys and a slowly-moving watercraft. The dominant SWT signal is the annual cycle (with a range of 26 °C and peak temperature in mid-July) while the diurnal range is as large as 4 °C during the spring season. Year-to-year variations in SWT are largest during the fall with over 1 °C anomalously warm (cold) departures from the 8-year monthly medians observed during fall 2001 (2006). The MODIS imagery provides an updated SWT climatology for operational weather forecasting applications (e.g., lake-effect snow storm prediction) as well as for input into operational and research numerical weather prediction models.

Flux of organic carbon in a riverine mangrove wetland in the Florida Coastal Everglades

Short-term (daily) and seasonal variations in concentration and flux of dissolved organic carbon (DOC) were examined over 15 tidal cycles in a riverine mangrove wetland along Shark River, Florida in 2003. Due to the influence of seasonal rainfall and wind patterns on Shark River’s hydrology, samplings were made to include wet, dry and transitional (Norte) seasons. We used a flume extending from a tidal creek to a basin forest to measure vertical (vegetated soil/water column) and horizontal (mangrove forest/tidal creek) flux of DOC. We found significant (p < 0.05) variations in surface water temperature, salinity, conductivity, pH and mean concentration of DOC with season. Water temperature and salinity followed seasonal patterns of air temperature and rainfall, while mean DOC concentration was highest during the dry season (May), followed by the wet (October) and ‘Norte’ (December) seasons. This pattern of DOC concentration may be due to a combination of litter production and inundation pattern of the wetland. In contrast to daily (between tides) variation in DOC flux between the mangrove forest and tidal creek, daily variations of mean water quality were not significant. However, within-tide variation of DOC flux, dissolved oxygen content and salinity was observed. This indicated that the length of inundation and water source (freshwater vs. saltwater) variation across tidal cycles influenced water quality and DOC flux in the water column. Net DOC export was measured in October and December, suggesting the mangrove forest was a source of DOC to the adjacent tidal creek during these periods. Net annual export of DOC from the fringe mangrove to both the tidal creek and basin mangrove forest was 56 g C m−2 year−1. The seasonal pattern in our flux results indicates that DOC flux from this mangrove forest may be governed by both freshwater discharge and tidal range.

Discussion of ‘Isotopic variation in fossils and matrix of the Cretaceous Red Chalk at Speeton and South Ferriby, Yorkshire, England’ Proceedings, Vol. 52, part 1, pp. 107–112, 1998

S. F. Mitchell and C. J. Underwood write: We welcome the study of G. D. Price on the isotopic composition of fossils and matrix from the Red Chalk, but would like to make a few additional points that we feel relate to this work. Price quoted the works of Ditchfield & Marshall (1989) and Jeans et al. (1991) as references on the study of stable isotopic compositions of matrix (or bulk sediment samples) and micro-fossils from the Lower Chalk. The Ditchfield & Marshall study suggested that cyclic oscillations in oxygen isotopic compositions were related to lithology, with chalk beds deposited under warmer surface water conditions than the intervening marl beds (i.e., they represented carbonate productivity cycles). This interpretation has been subsequently accepted by many authors (e.g., Jeans et al. 1991, amongst others). Mitchell et al. (1997), however, demonstrated that the cyclical oscillation in oxygen isotope values in these rhythmic chalk–marl successions in the Lower Chalk was the result of differential cementation of the limestone beds (where cement was concentrated in large pores such as planktic foraminifera and calcispheres) and that there appeared to be very little primary difference between the isotopic composition of the chalks and the marls. Price (1998, p. 109) suggested that the variation in the oxygen isotopic composition of the belemnite Neohibilites [ sic ] might be due to surface water temperature variations related to Milankovitch forcing, particularly as “well developed rhythmicity that may be due to Milankovitch climatic forcing” (Mitchell, 1995) is present in the Red Chalk.

Thermal radiometry: a rapid means of determining surface water temperature variations in lakes and reservoirs

To obtain remotely sensed synoptic measurements of surface water temperatures, use has been made of a Heimann Radiometer (Model KT79). This instrument, sensitive to thermal infrared radiation in the 8–14 μm wavelength range of the electromagnetic spectrum is fitted with a telephoto lens and gives a restricted field of view at the water surface, enabling temperature estimation to ±0.2°C. For example, over a period of 1 h it was possible, from suitably selected vantage points, to record 475 point measurements of temperature over the entire surface of a reservoir some 1 km 2 in area (Embalse de Rioseco, northern Spain). Repeated sets of observations permitted the recognition of upwelling and sinking water masses. The technique enabled the detection of influx of cold water from springs along a geological fault zone in the Embalse de Tanes. Additionally, the inception and the temporal and spatial evolution of an influent plunging plume was monitored using this equipment. Although thermal radiometry is restricted to the measurement of surface water temperatures, its speed of data acquisition over a wide area should enhance appreciation of the thermal behaviour of lakes and provide an important complement to existing techniques.

Could deep subantarctic convection feed the world deep basins during the Last Glacial Maximum?

Simple box model calculations are used to simulate the oceanic circulation during the last glacial maximum (LGM). These experiments show that the main features of the δ13C and Δ14C distributions and of the lysocline depth may be explained by a circulation pattern very different from the modem one. Intermediate and upper deep waters were produced in the North Atlantic Ocean, whereas deep waters of Subantarctic Mode type, forming at the northern edge of the Subantarctic convergence, invaded the main oceanic basins. The Southern Ocean, mainly self ventilated, had a reduced deep component that flew southward along the East Pacific Ridge and the Australian west cost. The thermodynamic fractionation that occurs during air‐sea exchange has only contributed slightly to the glacial deep δ13C distribution through surface water temperature variations.

Early Late Pliocene biochronology and surface water temperature variations in the Mediterranean

A high-resolution magnetobiostratigraphy is presented for the early Late Pliocene in Sicily. Paleomagnetic measurements on samples from 100 stratigraphic levels provide an unprecedented high-quality polarity sequence which extends from the upper reversed Gilbert to the upper normal Gauss subchron. The resultant chronology for the early Late Pliocene provides ages for the following principal Mediterranean bioevents: (1) FOD Globorotalia crassaformis at 3.40 Ma (2) prolonged absence of Globorotalia puncticulata between 3.38 and 3.16 Ma (3) LOD Uvigerina rutila at 3.16 Ma (4) LOD Sphaeroidinellopsis seminulina at 3.07 Ma (5) LOD Globoquadrina altispira at 3.04 Ma (6) LOD Cibicides italicus at 2.96 Ma. Summer and winter surface water temperature estimates for the period 3.50 to 2.92 Ma are based on the abundances of Globigerinoides sacculifer and Globorotalia puncticulata in 111 samples with an average resolution of some 5000 years. Short-term variations in temperature of the surface water and in colour and carbonate content of the sediment are primarily controlled by the equinoxal precession. A higher seasonality during deposition of the grey-coloured, carbonate-poor facies suggests that at that time the summer solstice occurred near perihelion, whereas an inverse alignment occurred at the time of deposition of white-coloured, carbonate-rich layers. This phase-relationship between the precession cycle and grey-coloured layers is also valid for the sapropels which began to intercalate in the grey-coloured layers at 2.94 Ma. Long-term changes in surface water temperatures include a warming between 3.38 and 3.18 Ma followed by a cooling from 3.18 to 3.03 Ma. The warming of Mediterranean surface waters at 3.38 Ma is believed to be associated with the final closure of the Isthmus of Panama. Consequent strengthening of the Gulf Stream injected larger volumes of warm surface water into the North Atlantic Drift and eastern boundary current and this caused surface water temperatures in the mid to high-latitude northeast Atlantic and Mediterranean to rise. The subsequent climatic cooling at 3.18 Ma is linked to a first stage of Northern Hemisphere continental ice growth.

Seasonal stable isotopic variations in living planktonic foraminifera from bermuda plankton tows

Seasonal variations in surface water temperature and the 18O/ 16O ratios of calcite tests of living planktonic foraminifera collected in the upper 10 mare are coincident in the Sargasso Sea off Bermuda. The δ 18O of seasonally restricted Globorotalia truncatulinoides and Globigerinoides ruber (pink and white) may be used to determine the seasonal temperature contrast of the oceans in the past. A preliminary model based on yearly absolute abundance and isotopic composition of these two species is able to approximate the composite δ 18O of fossil specimens of these species. Carbon and oxygen isotopic compositions of most species are size-dependent, with the largest differences occuring in δ 13C as a function of size. The calcite tests of all living species were depleted in δ 13C relative to the δ 13C of total dissolved CO 2 at 0 and 50 m, with no seasonal pattern in δ 13C being discernible in any species. In almost all cases, fossil specimens from box core sediments are significantly enriched in δ 13C and slightly enriched in δ 18O relative to their counterparts in the living fauna because the sediment populations are generally composed of larger-sized specimens compares to the plankton. of larger-size specimens compared to the plankton.