Rising Sea Surface Temperatures Research Articles

Rapid biogeographical plankton shifts in the North Atlantic Ocean

AbstractLarge‐scale biogeographical changes in the biodiversity of a key zooplankton group (calanoid copepods) were detected in the north‐eastern part of the North Atlantic Ocean and its adjacent seas over the period 1960–1999. These findings provided key empirical evidence for climate change impacts on marine ecosystems at the regional to oceanic scale. Since 1999, global temperatures have continued to rise in the region. Here, we extend the analysis to the period 1958–2005 using all calanoid copepod species assemblages (nine species assemblages based on an analysis including a total of 108 calanoid species or taxa) and show that this phenomenon has been reinforced in all regions. Our study reveals that the biodiversity of calanoid copepods are responding quickly to sea surface temperature (SST) rise by moving geographically northward at a rapid rate up to about 23.16 km yr−1. Our analysis suggests that nearly half of the increase in sea temperature in the northeast Atlantic and adjacent seas is related to global temperature rises (46.35% of the total variance of temperature) while changes in both natural modes of atmospheric and oceanic circulation explain 26.45% of the total variance of temperature. Although some SST isotherms have moved northwards by an average rate of up to 21.75 km yr−1 (e.g. the North Sea), their movement cannot fully quantify all species assemblage shifts. Furthermore, the observed rates of biogeographical movements are far greater than those observed in the terrestrial realm. Here, we discuss the processes that may explain such a discrepancy and suggest that the differences are mainly explained by the fluid nature of the pelagic domain, the life cycle of the zooplankton and the lesser anthropogenic influence (e.g. exploitation, habitat fragmentation) on these organisms. We also hypothesize that despite changes in the path and intensity of the oceanic currents that may modify quickly and greatly pelagic zooplankton species, these organisms may reflect better the current impact of climate warming on ecosystems as terrestrial organisms are likely to significantly lag the current impact of climate change.

A GA-based Band Selection Algorithm for Hyper-spectral Image Classification

We studied on the relationship between oceanic variation in the offshore and abnormal sea surface temperature rise in the coastal area of the Yellow Sea using a variety of satellite and in-situ data during winter 2004. In results of the satellite data, the average value of sea surface temperature in the Yellow Sea for 2003 was , and the average value of sea surface temperature for 2004 was . It was higher than those of the last year about . In results of the in-situ data, the average value of surface layer temperature in the Yellow Sea for 2003 was , and the average value of surface layer temperature for 2004 was . In the same satellite data, it was higher than those of the last year about . In results of the T-S diagram, we divided definitely into water mass of the Yellow Sea and the East China Sea in 2003. But we didn't divide definitely into water mass of the Yellow Sea and the East China Sea in 2004. The average values of air temperature and wind speed for 2003 were and 4.81 m/s, respectively. And, the average values of air temperature and wind speed for 2004 were and 4.52 m/s, respectively. So, These were similar. But the wind directions for 2003 were superior northwestern wind, and the wind directions for 2004 were various northern wind. The wind directions were different from each other. Therefore, the abnormal sea surface temperature rise in the coastal area of the Yellow Sea during winter 2004 were better related to oceanic variation in the offshore than influences of atmosphere. In the future, We will do in-depth study for these.

Microsatellite loci for assessing genetic diversity, dispersal and clonality of coral symbionts in ‘stress‐tolerant’ clade D Symbiodinium

Reef corals harbouring clade D Symbiodinium spp. (endosymbiotic dinoflagellates) appear more tolerant of environmental stress. As sea surface temperatures rise, symbioses involving Symbiodinium D may increase in prevalence. For this reason, eight polymorphic microsatellite loci were developed for clade D Symbiodinium. From the analysis of 132 samples originating from cnidarian hosts in the Atlantic, Pacific and Indian Oceans, 4 to 35 alleles were found at each haploid locus and diversity indices ranged from 0.35 to 0.97. Population genetic analyses of these symbionts should reveal how environmental perturbations affect genetic diversity, geographical distributions, and possible host-range expansions to new coral species.

군자 시험배수구역 합류식 하수관거시스템의 일일하수량 및 직접유출량 산정

A localized torrential rainfall and flash floods which are more frequently occurred by extraordinary atmospheric phenomena and rising sea surface temperature require more hydrological data collecting and analysis for small watershed. Urban watershed hydrological data monitoring system is needed because of big flood potential damage and lack of urban watershed hydrological data. Therefore, Urban Flood Disaster Management Research Center operates small experimental catchments(Sinnae1, Gunja, and Children`s Park) observing and analyzing hydrological data(rainfall, stage, and discharge). In this study, the discharge of combined sewage for Gunja experimental drainage is analyzed with weekly data and day of the week data. Through several analyses in analyzing the urban runoff characteristics and managing the urban sewage system, direct runoff is calibrated and verified by the estimated values of rainfall-runoff model(SWMM).

Recruitment Variability of Small Pelagic Fish Populations in the Kuroshio-Oyashio Transition Region of the Western North Pacific

Climatic and ecosystem changes in the transition region between the subarctic Oyashio and the subtropical Kuroshio Extension fronts may be the key to understanding recruitment variability of small pelagic fish populations in the Pacific waters off Japan. The transition region is characterized by complex oceanographic structure with the meandering fronts, eddies and streamers creating large spatial and temporal variability in the environment. Juveniles of small pelagic fishes such as Japanese sardine (Sardinops melanostictus), Pacific saury (Cololabis saira), and Japanese anchovy (Engraulis japonicus) migrate from the subtropical Kuroshio Current area to the subarctic Oyashio Current area across the transition region. A precipitous decline in number of age 0 recruits of Japanese sardine after the end of 1980s appears to be related to the extremely high mortality rate of young-of-the-year fish in the transition region. In contrast, populations of Pacific saury and Japanese anchovy increased after 1988. These synchronous changes in populations seem to be associated with the weakening of the Aleutian Low Pressure in the North Pacific and weakening of the Oyashio Current in winter, and a sea surface temperature (SST) rise in the Kuroshio-Oyashio transition region in spring. The contrasting responses of the fish populations to the SST rise can be explained by different temperature preference in terms of growth rate in larval and early juvenile stages; cool temperatures are preferred by sardine and warm temperatures are preferred by saury and anchovy.

A possible role for unstable coupled waves affected by resonance between Kelvin waves and seasonal warming in the development of the strong 1997–1998 El Niño

Time-varying air–sea coupled processes in the central to eastern equatorial Pacific associated with strong El Niño development during the 1997–1998 period are examined using a newly developed reanalysis dataset obtained from four-dimensional variational ocean–atmosphere coupled data assimilation experiments. The time series of this data field exhibits realistic features of El Niño evolution. Our analysis indicates that resonance between eastward-propagating oceanic downwelling Kelvin waves and the seasonal rise of sea-surface temperature (SST) in the central to eastern equatorial Pacific generates relatively persistent high SST conditions accompanied by a deeper thermocline and more relaxed easterly winds than usual. The surface condition resulting from the wave-seasonal SST resonance represents a preconditioned state that leads to an enhancement in incident downwelling Kelvin waves to levels sufficient to induce large-amplitude unstable coupled waves in the central to eastern equatorial region. Heat balance estimates using our reanalysis dataset suggest that the unstable coupled waves are categorized within the intermediate regime of coupled Kelvin and Rossby waves and have the potential to grow rapidly. We argue that the seasonal resonance and the unstable coupled waves should play crucial roles in the development of the largest historical El Niño event, which was recorded between late 1997 and early 1998.

Impacts of climate change and sea-level rise on cyclonic storm surge floods in Bangladesh

This paper describes the impacts of sea surface temperature (SST) rise and sea-level rise (SLR) on cyclonic storm surge flooding in western Bangladesh. A calibrated numerical hydrodynamic model was used to simulate surge wave propagation through the rivers and overland flooding. The model was calibrated with base condition (present climate), and then eight flooding scenarios of plausible future conditions were assessed by considering increased surge heights. Flooded area, flooding depth and surge intrusion length were computed by superimposing the predicted maximum water level information on a digital elevation model (DEM). This analysis showed that for a storm surge under 2 °C SST rise and 0.3 m SLR, flood risk area would be 15.3% greater than the present risk area and depth of flooding would increase by as much as 22.7% within 20 km from the coastline. Within the risk area, the study identified 5690 km 2 land (22% of exposed coast) as a high-risk zone (HRZ) where flooding of depth 1 m or more might occur, and people should move to nearby cyclone shelters during extreme cyclonic events. Predicted area of HRZ is 1.26 times the currently demarcated HRZ. It was estimated that 320 additional shelters are required to accommodate people in the newly identified HRZ. This information would be of value to policy and decision makers for future shelter planning and designing shelter heights.

Historical deadly typhoons in the Philippines

, in China and Japan, are used. The physical mechanisms responsible for their development are complex and not fully understood, but it is known that they require high sea-surface temperatures (SST), a moderate Coriolis force, a pre-existent synoptic perturbation (normally a monsoon trough or easterly wave) and low wind shear (Fink and Speth, 1998; Galvin, 2008). The dependence on high sea tem-perature has opened the debate on a pos-sible increase in the frequency of tropical cyclones in a changing climate. It has been proposed that a rise in SST induced by the anthropogenic global warming has already led to a greater number of intense tropical cyclones in recent decades (Emanuel, 2005; Webster

Archipelago-wide coral recovery patterns since 1998 in the Chagos Archipelago, central Indian Ocean

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 362:109-117 (2008) - DOI: https://doi.org/10.3354/meps07436 Archipelago-wide coral recovery patterns since 1998 in the Chagos Archipelago, central Indian Ocean C. R. C. Sheppard*, A. Harris, A. L. S. Sheppard Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK *Email: charles.sheppard@warwick.ac.uk ABSTRACT: Patterns of coral recovery are analysed across reefs of the Chagos Archipelago, which spans 400 × 250 km in the central Indian Ocean. This archipelago mostly lacks direct human impacts and is subject only to global changes such as a rise in sea surface temperature. Following very heavy coral mortality (mostly >90%) caused by the 1998 warming event, and despite 2 further sub-lethal bleaching events, the recovery of coral cover, colony numbers and juvenile recruitment has been good in many parts of the archipelago. There was little discrimination between atolls and depths, with a notable exception of 1 atoll where a repeat of heavy mortality had occurred in 2005. In 2006, coral cover was almost restored to pre-1998 values at most shallow sites, but had recovered much less in deeper waters. However, in shallow water, coral cover values alone are a poor indication of recovery, because present, shallow cover mainly comes from Acropora palifera and other corals that are largely encrusting in juvenile form, in contrast to their mature condition, in which they provide a 3-dimensional ‘forest’ structure. Recruitment of juvenile colonies in 2006 ranged from 6 to 28 m–2. Total juvenile density showed no significant pattern with atolls or with depth, but, taking each genus of juveniles in turn, many genera showed a marked depth preference. No shift was observed towards algal domination, or to assemblages dominated by Porites or faviids, as has been reported elsewhere. Recovery in Chagos 8 yr after massive coral and soft coral mortality is discussed in relation to an absence of other, locally manageable factors such as pollution, over-fishing and sedimentation. KEY WORDS: Coral reef · Coral bleaching · Recovery · Sea surface temperature Full text in pdf format PreviousNextCite this article as: Sheppard CRC, Harris A, Sheppard ALS (2008) Archipelago-wide coral recovery patterns since 1998 in the Chagos Archipelago, central Indian Ocean. Mar Ecol Prog Ser 362:109-117. https://doi.org/10.3354/meps07436 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 362. Online publication date: June 30, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.

Variability and Trend of North West Australia Rainfall: Observations and Coupled Climate Modeling

Abstract Since 1950, there has been an increase in rainfall over North West Australia (NWA), occurring mainly during the Southern Hemisphere (SH) summer season. A recent study using twentieth-century multimember ensemble simulations in a global climate model forced with and without increasing anthropogenic aerosols suggests that the rainfall increase is attributable to increasing Northern Hemisphere aerosols. The present study investigates the dynamics of the observed trend toward increased rainfall and compares the observed trend with that generated in the model forced with increasing aerosols. It is found that the observed positive trend in rainfall is projected onto two modes of variability. The first mode is associated with an anomalously low mean sea level pressure (MSLP) off NWA instigated by the enhanced sea surface temperature (SST) gradients toward the coast. The associated cyclonic flows bring high-moisture air to northern Australia, leading to an increase in rainfall. The second mode is associated with an anomalously high MSLP over much of the Australian continent; the anticyclonic circulation pattern, over northern Australia, determines that when rainfall is anomalously high, west of 130°E, rainfall is anomalously low east of this longitude. The sum of the upward trends in these two modes compares well to the observed increasing trend pattern. The modeled rainfall trend, however, is generated by a different process. The model suffers from an equatorial cold-tongue bias: the tongue of anomalies associated with El Niño–Southern Oscillation extends too far west into the eastern Indian Ocean. Consequently, there is an unrealistic relationship in the SH summer between Australian rainfall and eastern Indian Ocean SST: the rise in SST is associated with increasing rainfall over NWA. In the presence of increasing aerosols, a significant SST increase occurs in the eastern tropical Indian Ocean. As a result, the modeled rainfall increase in the presence of aerosol forcing is accounted for by these unrealistic relationships. It is not clear whether, in a model without such defects, the observed trend can be generated by increasing aerosols. Thus, the impact of aerosols on Australian rainfall remains an open question.

Climate variability, biological control and an insect pest outbreak on Australia’s Coral Sea islets: lessons for invertebrate conservation

Distant tropical coral sand islets in the Coral Sea have remained isolated from major human interference since their relatively recent inception. As a result they have highly impoverished faunas and floras consisting only of species capable of long distance dispersal. Despite this bias, they have established some degree of stability or equilibrium. In the 1990s, it became apparent that a scale insect, Pulvinaria urbicola Cockerell and at least one species of attendant ant, Tetramorium bicarinatum (Nylander) were undergoing a population explosion on two of these islets causing damage to Pisonia grandis, a tree important as a nesting site for sea birds. The same phenomenon as in the Coral Sea, (Coringa Herald group), was recorded about the same time in the Capricorn group of islets (Great Barrier Reef), on Palmyra Atoll and Samoa in the Pacific and in the Seychelles (Indian Ocean). Control measures, the application of systemic insecticides, poisoning of attendant ants and introduction of biological control agents were applied to some islands. Pest numbers subsequently fell, often within months, even where no control measures were applied, suggesting that the population decline was a natural phenomenon on some sites and not the result of recent invasions. It is suggested that climate variability is likely to be a contributing factor. Rising sea surface temperatures that reduce prey available to sea birds so causing a lower nitrogen input to soils during nesting activities, together with drier conditions, are likely to have put Pisonia trees under stress. Stressed trees mobilise nutrients making them more vulnerable to attack by herbivores. If climate variability is an indirect cause of the pest outbreak, it is important to carefully assess the benefits and disadvantages, both environmentally and economically, of any control measures, especially when biological control agents are concerned, the effects of which are irreversible.

Effect of interannual variations in sea-surface temperature on egg-laying parameters of black-tailed gulls (Larus crassirostris) at Teuri Island, Japan

Sea-surface temperature (SST) directly and indirectly affects the distribution and abundance of prey species for seabirds, so we expect variation in SST to be associated with variation in seabird life history traits. In black-tailed gulls (Larus crassirostris) at Teuri Island in northern Hokkaido, Japan, we investigated the diet of the gulls prior to egg laying in 2004 and 2005, and examined the influences of SST in March or April, when the gulls congregate in the colony, on egg-laying parameters using 13 years of data (1992–2004). The gulls fed on krill (Thysanoessa inermis) and fish prior to the egg laying. Mean first egg dates and clutch sizes were significantly and quadratically related to SST anomalies in March, but were not influenced by SST anomalies in April. There was no significant effect of SSTs in either March or April on egg volume. Sea-surface temperature anomalies in March of the years of early laying (−1 to 1°C) were higher than those in 2001 (−2.2°C), but lower than those in 1992 (+1.2°C) and 2004 (+1.1°C). Thysanoessa inermis congregates to spawn at the sea surface, when SSTs rise 3−4°C. Thus, a mismatch between food availability and the timing of egg production in the gulls could have occurred in these 3 years. This study suggests that SST fluctuations prior to laying are important in breeding success of black-tailed gulls.

Gulf Stream and ENSO Increase the Temperature Sensitivity of Atlantic Tropical Cyclones

Abstract Controversy exists over the role of the recent rise in sea surface temperatures (SST) and the frequency of tropical cyclones or hurricanes. Here, 135 yr of observational records are used to demonstrate how sea surface temperature, sea level pressure, and cyclone numbers are linked. A novel wavelet-lag coherence method is used to study cause and effect relations over a large space of time scales, phase lags, and periods. It is found that SST and cyclones are not merely correlated, but are in a negative feedback loop, where rising SST causes increased numbers of cyclones, which reduce SST. This is statistically most significant at decadal and not at longer periods, which is contrary to expectations if long-period natural cycles are important in driving cyclone numbers. Spatial relationships are examined using phase-aware teleconnections, which at the dominant decadal period show the in-phase behavior of the Atlantic SST in the Gulf Stream region, reflecting the role of the transportion of heat northward from the tropical Atlantic. At 5-yr periods there is significant coherence when SST leads cyclones by 2 yr, and this is associated with tropical ENSO activity such that, as predicted, increasing numbers of El Niños cause fewer Atlantic cyclones. The pattern of coherence existing since 1970 strongly favors the decadal coherence band, and despite growing coherence at higher frequencies, there is none at the 5-yr band, perhaps explaining why the observed sensitivity between SST and cyclones is larger than that from general circulation model (GCM) predictions and becoming greater.

Changes in the large‐scale features associated with the Indian summer monsoon in the recent decades

AbstractThe inter‐annual variability of the Indian summer monsoon rainfall (ISMR) has been examined in association with the variability of surface temperature, the mean sea level pressure (MSLP), the tropospheric geopotential height, and wind patterns over the globe to study the changes in the large‐scale features associated with Indian summer monsoon (ISM) in the recent decades. The data for the study have been considered from 1949–2005 (for a period of 57 years). It has been found that, during the recent decades, the El Nino‐Southern Oscillation (ENSO) relationship over ISMR has weakened while the northwest (NW) of North Atlantic sea surface temperature (SST) relationship has increased. A physical mechanism for the relationship of North Atlantic SST with ISMR is proposed, by which during the excess years of ISMR, the SST over NW of North Atlantic is above normal. The rise in SST is the consequence of intensification and a cell‐type shaped Azores high with isobars parallel to the east coast of North America, which drives a subtropical oceanic gyre (Gulf stream) transporting equatorial warm water NW of North Atlantic. The Azores high act as a source of downstream Rossby wave train over Eurasian region having barotropic structure consisting of a successive pressure trough and ridge. The Rossby wave may be associated with intensifying the low surface pressure anomaly over the Iranian landmass, which intensify the monsoon current over the Indian region. Copyright © 2008 Royal Meteorological Society

Lagrangian Diagnostics of Tropical Deep Convection and Its Effect upon Upper-Tropospheric Humidity

AbstractThis study combines geostationary water vapor imagery with optical cloud property retrievals and microwave sea surface observations in order to investigate, in a Lagrangian framework, (i) the importance of cirrus anvil sublimation on tropical upper-tropospheric humidity and (ii) the sea surface temperature dependence of deep convective development. Although an Eulerian analysis shows a strong spatial correlation of ∼0.8 between monthly mean cirrus ice water path and upper-tropospheric humidity, the Lagrangian analysis indicates no causal link between these quantities. The maximum upper-tropospheric humidity occurs ∼5 h after peak convection, closely synchronized with the maximum cirrus ice water path, and lagging behind it by no more than 1.0 h. Considering that the characteristic e-folding decay time of cirrus ice water is determined to be ∼4 h, this short time lag does not allow for significant sublimative moistening. Furthermore, a tendency analysis reveals that cirrus decay and growth, in terms of both cloud cover and integrated ice content, is accompanied by the drying and moistening of the upper troposphere, respectively, a result opposite that expected if cirrus ice were a primary water vapor source. In addition, it is found that an ∼2°C rise in sea surface temperature results in a measurable increase in the frequency, spatial extent, and water content of deep convective cores. The larger storms over warmer oceans are also associated with slightly larger anvils than their counterparts over colder oceans; however, anvil area per unit cumulus area, that is, cirrus detrainment efficiency, decreases as SST increases.

Timing and magnitude of early Aptian extreme warming: Unraveling primary δ18O variation in indurated pelagic carbonates at Deep Sea Drilling Project Site 463, central Pacific Ocean

In order to elucidate early Aptian marine paleotemperature evolution across the period of enhanced organic carbon (C org)-burial [Oceanic Anoxic Event (OAE) 1a], stable isotope analyses were performed on pelagic limestones at Deep Sea Drilling Project Site 463, central Pacific Ocean. The δ 18O data exhibit a distinct anomaly by ~ − 2‰ spanning the OAE 1a interval (i.e., a ~ 6 m-thick, phytoplanktonic C org-rich unit constrained by magneto-, bio- and δ 13C stratigraphy). Elucidation of paleotemperature significance of the δ 18O shift is made by taking account of recent Sr/Ca evidence at the same section, which revealed that geochemical signals in carbonate-poor lithologies are relatively unaltered against burial diagenesis. By discriminating δ 18O values from carbonate-poor samples (CaCO 3 contents = 5–30 wt.%), it appears that an abrupt rise in sea-surface temperatures (SSTs) by 8 °C (= − 1.7‰ shift in δ 18O) occurred immediately before OAE 1a, whereas a cooling mode likely prevailed during the peak C org-burial. In terms of its stratigraphic relationship as to the C org-rich interval and to a pronounced negative δ 13C excursion, as well as its timescale, the observed SST rise resembles those associated with the Paleocene–Eocene thermal maximum and, more strikingly, Jurassic Toarcian OAE. This observation is consistent with the hypothesis that these paleoenvironmental events were driven by a common causal mechanism, which was likely initiated by the greenhouse effect via massive release of CH 4 or CO 2 from the isotopically-light carbon reservoir and terminated by a negative productivity feedback.

Diurnal sea surface temperature variation and its impact on the atmosphere and ocean: A review

The importance of the diurnal variability of sea surface temperature (SST) on air-sea interaction is now being increasingly recognized. This review synthesizes knowledge of the diurnal SST variation, mainly paying attention to its impact on the atmosphere or the ocean. Diurnal SST warming becomes evident when the surface wind is weak and insolation is strong. Recent observations using satellite data and advanced instruments have revealed that a large diurnal SST rise occurs over wide areas in a specific season, and in an extreme case the diurnal amplitude of SST exceeds 5 K. The large diurnal SST rise can lead to an increase in net surface heat flux from the ocean of 50–60 Wm−2 in the daytime. The temporal mean of the increase exceeds 10 Wm−2, which will be non-negligible for the atmosphere. A few numerical experiments have indicated that the diurnal SST variation can modify atmospheric properties over the Pacific warm pool or a coastal sea, but the processes underlying the modification have not yet been investigated in detail. Furthermore, it has been shown that the diurnal change of ocean mixing process near the surface must be considered correctly in order to reproduce SST variations on an intraseasonal scale in a numerical model. The variation of mixed-layer properties on the daily scale is nonlinearly related to the intraseasonal variability. The mixed-layer deepening/shoaling process on the daily scale will also be related to biological and material circulation processes.

Impact of scaling behavior on tropical cyclone intensities

Theory suggests tropical cyclone maximum potential intensity increases with increasing ocean temperature. However, most tropical cyclones fail to achieve this maximum intensity. Instead, empirical studies suggest that tropical cyclone intensities are uniformly distributed between this maximum potential intensity and an intensity that marks the transition between tropical storm and hurricane scaling regimes. Here it is shown that this transition shifts significantly on interannual to interdecadal time scales in both the North Atlantic and Western North Pacific basins. The intensity at which this transition occurs effectively determines the fraction of tropical cyclones entering the hurricane scaling regime, and as such, strongly impacts the fraction of tropical cyclones that become intense. The increase in the fraction of intense tropical cyclones in recent decades results primarily from a shift in this scaling transition toward weaker winds rather than an increase in the maximum potential intensity directly attributable to rising sea surface temperatures. This scaling transition is shown to vary with sea surface temperature (SST) anomalies in the tropical cyclone main development regions relative to tropical mean SST anomalies, in contrast to the maximum potential intensity which varies with the SST itself.

Warm arctic continents during the Palaeocene–Eocene thermal maximum

The Palaeocene–Eocene Thermal Maximum (PETM; ∼55.5 Ma) is a geologically relatively brief episode of extreme warmth. Both deep and surface ocean temperatures increased by up to 5 °C in equatorial waters and up to 8 °C in mid and high latitude waters. From the continents, the annual mean air temperature response during the PETM is still largely unknown, mainly due to a lack of quantitative temperature proxies and sufficient suitable, continuous high resolution records. Recently, a new proxy for continental temperature reconstructions has been proposed, based on the distribution of membrane lipids of bacteria in present-day soils [ J.W.H. Weijers, S. Schouten, J.C. van den Donker, E.C. Hopmans, J.S. Sinninghe Damsté (2007) Environmental controls on bacterial tetraether membrane lipid distribution in soils, Geochimica et Cosmochimica Acta 71, 703–713] and shown to reconstruct annual mean air temperature. In this study we applied this new proxy in an attempt to reconstruct the air temperature in high latitude continental areas during the PETM by analysis of a marine sedimentary sequence obtained from the Lomonosov Ridge in the central Arctic Ocean (Integrated Ocean Drilling Program Expedition 302, Site 004, Hole A). The results indicate a warming of ∼8 °C above background values of ∼17 °C. This warming is coincident with a similar rise in sea surface temperatures documented earlier. Our results thus further confirm the warm conditions in the Arctic, and point to a strongly reduced latitudinal temperature gradient during the PETM.

Objectively Analyzed Air–Sea Heat Fluxes for the Global Ice-Free Oceans (1981–2005)

A 25-yr (1981–2005) time series of daily latent and sensible heat fluxes over the global ice-free oceans has been produced by synthesizing surface meteorology obtained from satellite remote sensing and atmospheric model reanalyses outputs. The project, named Objectively Analyzed Air–Sea Fluxes (OAFlux), was developed from an initial study of the Atlantic Ocean that demonstrated that such data synthesis improves daily flux estimates over the basin scale. This paper introduces the 25-yr heat flux analysis and documents variability of the global ocean heat flux fields on seasonal, interannual, decadal, and longer time scales suggested by the new dataset. The study showed that, among all the climate signals investigated, the most striking is a long-term increase in latent heat flux that dominates the data record. The globally averaged latent heat flux increased by roughly 9 W m−2 between the low in 1981 and the peak in 2002, which amounted to about a 10% increase in the mean value over the 25-yr period. Positive linear trends appeared on a global scale, and were most significant over the tropical Indian and western Pacific warm pool and the boundary current regions. The increase in latent heat flux was in concert with the rise of sea surface temperature, suggesting a response of the atmosphere to oceanic forcing.