Sea Surface Temperature Shifts Research Articles

How Atmospheric Forcing Frequency, Horizontal and Vertical Grid Resolutions Impact Mesoscale Eddy Evolution in a Numerical Model

AbstractSeasonal evolution of both surface signature and subsurface structure of a Mediterranean mesoscale anticyclones is assessed using the Coastal and Regional Ocean Community high‐resolution numerical model with realistic background stratification and fluxes. In good agreement with remote‐sensing and in‐situ observations, our numerical simulations capture the seasonal cycle of the anomalies induced by the anticyclone, both in the sea surface temperature (SST) and in the mixed layer depth (MLD). The eddy signature on the SST shifts from warm‐core in winter to cold‐core in summer, while the MLD deepens significantly in the core of the anticyclone in late winter. Our sensitivity analysis shows that the eddy SST anomaly can be accurately reproduced only if the vertical resolution is high enough (∼4 m in near surface) and if the atmospheric forcing contains high‐frequency. In summer with this configuration, the vertical mixing parameterized by the k − ϵ closure scheme is three times higher inside the eddy than outside the eddy, and leads to an anticyclonic cold core SST anomaly. This differential mixing is explained by near‐inertial waves, triggered by the high‐frequency atmospheric forcing. Near‐inertial waves propagate more energy inside the eddy because of the lower effective Coriolis parameter in the anticyclone core. On the other hand, eddy MLD anomaly appears more sensitive to horizontal resolution, and requires SST retroaction on air‐sea fluxes. These results detail the need of high frequency forcing, high vertical and horizontal resolutions to accurately reproduce the evolution of a mesoscale eddy.

Using long‐term data series to design adequate protected areas that ensure the conservation of inconspicuous small petrel species

Abstract Marine protected areas (MPAs) are widely used tools for conservation and management. Their correct delimitation is challenging, especially when the target species are small, elusive and inconspicuous, as little data are generally available to adequately assess their distribution at sea. Therefore, currently designated MPAs may not effectively cover key areas for small seabirds, particularly during migration and wintering seasons. We used ensemble species distribution models (ESDMs) on a 15‐year time‐series data set of at‐sea census along the Atlantic Iberian arc to predict the potential distribution of the smallest European seabird, the European storm‐petrel (Hydrobates pelagicus), and compare it with official marine special protection areas (SPAs). Occurrence of European storm‐petrel was related to shifts in sea surface temperature, and to small distances from the coast over the continental shelf. Most relevant area for the species in the Atlantic Iberian arc was west‐central Portugal to north‐western coast of the Iberian Peninsula, with an additional key area in the Gulf of Cádiz. Both zones host significant SPAs, but they inadequately cover key areas for European storm‐petrels. Our findings support extending marine SPAs in the Atlantic Iberian arc to ensure their effective protection. The distribution of the species expands over the years, varying in both size and location. These changes might be attributed to dynamic oceanographic variables, such as sea surface temperature and biomass of micronekton, which seem to play a significant role in their foraging behaviour. Synthesis and applications. Our study highlights the importance of analysing long time series and ESDMs to design adequate protected areas, which ensure the conservation of small and highly mobile species such as storm petrels. Our results should be considered by decision‐makers to prioritise and update marine protected areas, while incorporating the dynamic nature of the ocean within an ecosystem‐based approach.

Understanding Models' Global Sea Surface Temperature Bias in Mean State: From CMIP5 to CMIP6

AbstractThis paper evaluates sea surface temperature (SST) biases of coupled models participating in Coupled Model Intercomparison Project Phase 5 (CMIP5) and CMIP6. Overall, CMIP6 models perform better than CMIP5 ones in reproducing SST climatology, with lower multi‐model ensemble mean (MME) globally averaged absolute bias (1.17 vs. 1.31 K). MME bias in global mean annual SST shifts from cooling (−0.09 ± 0.52 K) to warming (0.23 ± 0.60 K). Regionally, in CMIP6 cooling biases over the Northwest Pacific and North Atlantic are reduced by 20% and 18%, while warming biases over the Northeast Pacific, Southeast Atlantic and Southern Ocean are increased by 25%, 16% and 107% respectively. These changes are mainly attributed to the combined effects from aggravated positive (or alleviated negative) bias in clear‐sky surface downward longwave radiation, and alleviated negative bias in cloud radiative effect, partially reduced by enhanced cooling bias in clear‐sky surface downward shortwave radiation.

Geochemical significance of Acropora death assemblages in the northern South China Sea: Implications for environmental reconstruction using branching corals

The geochemistry preserved in coral skeletons provides access to pre-instrumental records of environmental changes. While a variety of proxies have been established for coral paleoclimatology, their applications to the use of Acropora to generate longer-term reconstructions have been studied less. Here, we examine the geochemical proxies (i.e., Sr/Ca, Li/Mg, δ18O, δ13C, δ11B, and B/Ca) of dead Acropora assemblages collected from a fringing reef off Hainan Island in the northern South China Sea. These samples have been precisely dated using UTh isotopes and record reef development episodes since the mid-Holocene, allowing us to assess their potential as paleoclimate archives. The sea surface temperature (SST) trend reconstructed by Sr/Ca and Li/Mg exhibits better consistency with each other, and they have recorded the SST shifts around 5–4 ka BP and the subdued variability during the Medieval Climate Anomaly (MCA), whereas the δ18O-SST record exhibits less clear variations over the past 7000 years. However, the universal Li/Mg-SST calibration tends to underestimate the SST reconstruction from tropical corals, highlighting the importance of using a site- and species-specific calibration of the Li/Mg-SST. Boron systematics are used to reconstruct the carbonate chemistry of coral calcifying fluid (CF), which reveals significant differences between the ancient and modern corals. The pH of the coral CF (pHcf) is significantly lower in the modern Acropora compared to the ancient corals, with a mean difference of ~0.08 pH, corroborating the pronounced influence of ocean acidification on the coral CF chemistry. The dissolved inorganic carbon of the coral CF (DICcf) is also lower for modern Acropora, and this decreasing trend seems to have persisted over the past 7000 years. In addition, the skeletal δ13C is closely related to the CF carbonate chemistry, highlighting the intrinsic relationship between the coral internal carbon pool used for calcification and the up-regulation of the pHcf.

Interannual shifts in sea surface temperature and chlorophyl drive the relative abundance and group size of common bottlenose dolphins Tursiops truncatus on the Southeast Gulf of California

Despite being one of the most common odontocetes off Sinaloa (Mexican Pacific coast), basic studies on the ecology of common bottlenose dolphins (Tursiops truncatus) are scarce in the region. This study aimed to describe changes in the relative abundance, group size, and behavior of this species during 2007 – 2012. We used boat-based surveys and satellite images of sea surface temperature (SST) and chlorophyll-a (Chl-a) to model changes in dolphin relative abundance (RA) over time, using correlations in time series analyses. Overall, mean RA was 3.6 dolphins h-1 (SD = 8.0), and significantly higher RA (6.4 –16.7 dolphins h-1) occurred in 2008, 2011, 2012, which was concurrent with hydrographic effects of La Niña oceanographic conditions, as well as during the upwelling season (February – April) (SST: 17.3 – 25.0 °C; Chl-a: 3.7 – 21.4 mg m-3). Conversely, significantly lower RA values (0.5 – 3.8 dolphins h-1) occurred in 2007 and 2010 that were likely associated with El Niño effects on the biological productivity of the area (Chl-a: 0.3 – 7.6 mg m-3). We found significant correlations between monthly Chl-a and SST average values with mean bottlenose dolphins RA, and lags (22 – 29 days) in the trophic response to variations of the hydrographic parameters. Significantly larger dolphin groups were recorded during La Niña years possibly because of the higher availability of their prey. This hypothesis is supported by higher feeding frequencies (35 – 73%) observed during the upwelling seasons, especially during La Niña conditions, whereas the most frequent behavior throughout all other years was traveling (28 – 69%). Our results show that RA and group size of bottlenose dolphins inhabiting the waters off Sinaloa, Mexico, are likely influenced by the changes in hydrographic parameters, especially during extreme climatic events.

Male-Biased Sex Ratio of Adult-Sized Loggerhead Turtles (Caretta caretta) Migrating to High-Latitude Summer-Restricted Foraging Grounds in the Northwest Pacific1

Although part of the life history of loggerhead turtles (Caretta caretta) in the northwest Pacific population has been documented, there is still a paucity of data regarding their spatiotemporal ecology at the local level. The Sanriku Coast is known to be the high-latitude foraging grounds (39° N) for loggerhead turtles of the northwest Pacific population. This site is located far north from the northernmost loggerhead rookeries (>400 km) and more than 10 years of surveys have found that loggerhead turtles migrate there only in the summer. To better understand the spatiotemporal ecology of this population along the Sanriku Coast, the present study investigated the sex of 164 loggerhead turtles captured as bycatch along the Sanriku Coast between 2013 and 2017 by measuring the external morphology and serum testosterone concentrations. These analyses suggested that most of the adult-sized turtles in the Sanriku foraging grounds were males (few females), whereas both sexes of immature-sized turtles migrated to this Coast. This is possibly because migration to the Sanriku Coast is restricted to summer due to the seasonal sea surface temperature shift, and this period overlaps with the nesting period. Therefore, only immature turtles and adult males may be able to migrate. Understanding sex differences in spatiotemporal ecology should contribute to conservation practice in this population, where global warming, together with the turtle's temperature-dependent sex determination, can be expected to reduce the proportion of male hatchlings in the future.

Rain, rain, gone away: decreased growing-season rainfall for the dryland cropping region of the south-west of Western Australia

The shift in Indian Ocean sea surface temperatures in 1976 led to a change in rainfall for the broad-scale winter annual grain cropping and pasture region in the south-west of Western Australia (the WA wheatbelt). Agriculture in the eastern part the WA wheatbelt was particularly sensitive to the change in rainfall because it is a marginal area for agronomic production, with low rainfall before changes in sea surface temperature. A second shift in sea surface temperature occurred in 2000, but there has been no analysis of the resulting impact on rainfall in the eastern WA wheatbelt. An analysis of rainfall pre- and post-2000 was performed for sites in the eastern WA wheatbelt in three groups: 19 sites in the west, 56 central, and 10 east. The analysis found a decline in growing-season rainfall (i.e. April–October), especially during May–July, post-2000. Rainfall declines of 49.9 mm (west group), 39.1 mm (central group) and 28.0 mm (east group) represented respective losses of 20.1%, 17.4% and 14.2% of growing-season rainfall. Increases in out-of-season rainfall in the respective groups of 31.0, 33.6, and 50.7 mm (57.8%, 60.8% and 87.6%) meant that annual rainfall changes were smaller than growing-season losses. The west and central groups lost 17.5 and 6.16 mm annual rainfall, whereas the east group gained 15.6 mm. Analysis of wheat yield indicated reductions of 13.5% (west) and 9.90% (central) in the eastern WA wheatbelt; the small group of east sites had a potential yield gain of 8.9% arising from the increased out-of-season rainfall. Further, increased out-of-season rainfall will exacerbate weed and disease growth over the summer fallow.

A 1-Ma record of sea surface temperature and extreme cooling events in the North Atlantic: A perspective from the Iberian Margin

The Iberian Margin is a sensitive area to track high and low latitude processes, and is a key location to understand major past climatic and oceanographic changes. Here we present new biomarker data from IODP Site U1385 (“Shackleton site”) (1017–336 ka) that, when combined with existing data from Cores MD01-2443/4 (last 335 ka), allows us to assess the evolution of sea surface temperature (SST) and meltwater influx over the last 1 Ma at the Iberian Margin. Interglacial periods throughout the last 1 Ma show SST close to 20 °C, even during the so-called “luke-warm” interglacials that are marked by relatively low atmospheric CO2 concentrations. During glacial periods, extremely cold stadial events are recognized at the Iberian Margin, and are very likely related to meltwater discharges from the European and British-Irish ice sheets into the NE Atlantic, which were transported southwards by the Portugal Current. We subdivided the record into four intervals on the basis of the timing and the magnitude of these extremely cold stadials: 1) from 1017 to ∼900 ka, only minor sporadic freshwater input occurred during deglaciations; 2) from 900 to 675 ka extreme cold events occur as terminal stadial events at the beginning of the deglaciations, which results in abrupt deglacial SST shifts; 3) from 675 to 450 ka only a few, very short-lived events are recorded and seldom is there freshwater input at the Iberian Margin; 4) during the last 450 ka the extreme cold events occurred under full glacial conditions, with particularly severe events during MIS 6 and 8. We propose these mid –glacial events are associated with a strong discharges of European ice sheet (EIS). The fact that these extreme cold events do not coincide with deglaciations questions the role of European ice sheet discharges in triggering deglaciations.

Breakup of land‐fast sea ice in Lützow‐Holm Bay, East Antarctica, and its teleconnection to tropical Pacific sea surface temperatures

AbstractA large land‐fast sea ice breakup occurred in 2016 in Lützow‐Holm Bay, East Antarctica. The breakup caused calving from the Shirase Glacier Tongue. Although similar breakups and calving have been observed in the past, the timing and magnitudes are not well‐constrained. The ice's breakup latitude during 1997–2016 was analyzed to investigate the variables controlling breakup and examine correlation with local calving for a longer period. The breakup latitude in April had a persistently high correlation with sea surface temperature (SST) in the tropical Pacific, which exceeds correlations with local atmospheric variables. The years of five out of six observed calving events from the mid‐20th century can correspond to those of warm SST episodes and calving‐front retreat in the 1980s to warmer SST shift. Our proposed teleconnection between tropical SST and Antarctic sea ice could lead to better predictions of breakup and might impact the glacier flux for a wider region.

Seasonal trends and phenology shifts in sea surface temperature on the North American northeastern continental shelf

The northeastern North American continental shelf from Cape Hatteras to the Scotian Shelf is a region of globally extreme positive trends in sea surface temperature (SST). Here, a 33-year (1982–2014) time series of daily satellite SST data was used to quantify and map spatial patterns in SST trends and phenology over this shelf. Strongest trends are over the Scotian Shelf (>0.6°C decade–1) and Gulf of Maine (>0.4°C decade–1) with weaker trends over the inner Mid-Atlantic Bight (~0.3°C decade–1). Winter (January–April) trends are relatively weak, and even negative in some areas; early summer (May–June) trends are positive everywhere, and later summer (July–September) trends are strongest (~1.0°C decade–1). These seasonal differences shift the phenology of many metrics of the SST cycle. The yearday on which specific temperature thresholds (8° and 12°C) are reached in spring trends earlier, most strongly over the Scotian Shelf and Gulf of Maine (~ –0.5 days year–1). Three metrics defining the warmest summer period show significant trends towards earlier summer starts, later summer ends and longer summer duration over the entire study region. Trends in start and end dates are strongest (~1 day year–1) over the Gulf of Maine and Scotian Shelf. Trends in increased summer duration are >2.0 days year–1 in parts of the Gulf of Maine. Regression analyses show that phenology trends have regionally varying links to the North Atlantic Oscillation, to local spring and summer atmospheric pressure and air temperature and to Gulf Stream position. For effective monitoring and management of dynamically heterogeneous shelf regions, the results highlight the need to quantify spatial and seasonal differences in SST trends as well as trends in SST phenology, each of which likely has implications for the ecological functioning of the shelf.

Seasonal trends and phenology shifts in sea surface temperature on the North American northeastern continental shelf

Seasonal trends and phenology shifts in sea surface temperature on the North American northeastern continental shelf

Evidence for two abrupt warming events of SST in the last century

We have recently suggested that the warming in the sea surface temperature (SST) since 1900, did not occur smoothly and slowly, but with two rapid shifts in 1925/1926 and 1987/1988, which are more obvious over the tropics and the northern midlatitudes. Apart from these shifts, most of the remaining SST variability can be explained by the El Niño Southern Oscillation and the Pacific Decadal Oscillation (PDO). Here, we provide evidence that the timing of these two SST shifts (around 60 years) corresponds well to the quasi-periodicity of many natural cycles, like that of the PDO, the global and Northern Hemisphere annual mean temperature, the Atlantic Multi-decadal Oscillation, the Inter-Tropical Convergence Zone, the Southwest US Drought data, the length of day, the air surface temperature, the Atlantic meridional overturning circulation and the change in the location of the centre of mass of the solar system. In addition, we show that there exists a strong seasonal link between SST and ENSO over the tropics and the NH midlatitudes, which becomes stronger in autumn of the Northern Hemisphere. Finally, we found that before and after each SST shift, the intrinsic properties of the SST time series obey stochastic dynamics, which is unaffected by the modulation of these two shifts. In particular, the SST fluctuations for the time period between the two SST shifts exhibit 1/f-type long-range correlations, which are frequently encountered in a large variety of natural systems. Our results have potential implications for future climate shifts and crossing tipping points due to an interaction of intrinsic climate cycles and anthropogenic greenhouse gas emissions.

Long-term Changes in Sea Surface Temperature at Selected Locations in the Sea of Oman and the Arabian Sea off Oman

Long-term changes in the sea surface temperature (SST) at two locations off Oman were investigated using Hadley Center SST for the period 1961~2009. A mean annual increase in SST by 0.32℃ was noticed in the Sea of Oman while an increase of 0.53℃ was noticed in the western Arabian Sea. The shift in SST is higher off Muscat than off Masirah during the study period. The bi-modal variability of the SST in the study region is successfully simulated by a cyclic model developed utilizing SST data for 1961~2009 period. An increase in summer warming and decrease in winter cooling are evident in the annual SST distribution at both the locations. The decadal variability off Masirah in the western Arabian Sea showed that the standard deviation of SST switched its character post-1990. The SST variance in Sea of Oman showed a decadal-scale change but in western Arabian Sea, it was nearly unchanged until 1990 and rapidly declined post-1990 period. The large shifts in SST apparently caused higher variability in the sea surface height (SSH) anomalies post-1990 period.

The Aqua-Planet Experiment (APE): Response to Changed Meridional SST Profile

This paper explores the sensitivity of Atmospheric General Circulation Model (AGCM) simulations to changes in the meridional distribution of sea surface temperature (SST). The simulations are for an aqua-planet, a water covered Earth with no land, orography or sea- ice and with specified zonally symmetric SST. Simulations from 14 AGCMs developed for Numerical Weather Prediction and climate applications are compared. Four experiments are performed to study the sensitivity to the meridional SST profile. These profiles range from one in which the SST gradient continues to the equator to one which is flat approaching the equator, all with the same maximum SST at the equator. The zonal mean circulation of all models shows strong sensitivity to latitudinal distribution of SST. The Hadley circulation weakens and shifts poleward as the SST profile flattens in the tropics. One question of interest is the formation of a double versus a single ITCZ. There is a large variation between models of the strength of the ITCZ and where in the SST experiment sequence they transition from a single to double ITCZ. The SST profiles are defined such that as the equatorial SST gradient flattens, the maximum gradient increases and moves poleward. This leads to a weakening of the mid-latitude jet accompanied by a poleward shift of the jet core. Also considered are tropical wave activity and tropical precipitation frequency distributions. The details of each vary greatly between models, both with a given SST and in the response to the change in SST. One additional experiment is included to examine the sensitivity to an off-equatorial SST maximum. The upward branch of the Hadley circulation follows the SST maximum off the equator. The models that form a single precipitation maximum when the maximum SST is on the equator shift the precipitation maximum off equator and keep it centered over the SST maximum. Those that form a double with minimum on the equatorial maximum SST shift the double structure off the equator, keeping the minimum over the maximum SST. In both situations only modest changes appear in the shifted profile of zonal average precipitation. When the upward branch of the Hadley circulation moves into the hemisphere with SST maximum, the zonal average zonal, meridional and vertical winds all indicate that the Hadley cell in the other hemisphere dominates.

Dependency of typhoon intensity and genesis locations on El Niño phase and SST shift over the western North Pacific

The effects of the El Nino-Southern Oscillation (ENSO) phase and the shifting of the ENSO sea surface temperature (SST) on the intensity of tropical cyclones (TC) have been extensively investigated in terms of TC genesis locations in the western North Pacific (WNP). To advance the hypothesis for a relation of genesis location–intensity that the TC formation location hints its intensity, two cases have been compared, which include the phase of the decaying El Nino turning over to La Nina (type I) and the phase that recovers to a neutral condition (type II). In addition, the shift of ENSO SST to the central Pacific warming (CPW) from the East Pacific warming (EPW) has been examined. The genesis potential index (GPI) and the accumulated cyclone energy have been applied to compare the differences between the ENSO phase and the TC formation location. It was apparent that ENSO influences the WNP typhoon formation location depending on the cycle of the ENSO phase. In addition, the typhoon activity was affected by the zonal shift of the El Nino SST. The CPW, which has maximum SST over the central Pacific, tends to have a persistently high GPI over the WNP in September–November and June–August, demonstrating that the formation locations of strong TCs significantly shift southeastward compared with the EPW having SST maximum over the eastern Pacific. CPW years revealed a distinguishable relationship between the TC formation location and the TC between the tropical depression (TD) + tropical storm (TS) and the intense typhoon of category 4 + 5.

Modelling the impacts of environmental variation on the distribution of blue marlin, Makaira nigricans, in the Pacific Ocean

Abstract Su, N-J., Sun, C-L., Punt, A. E., Yeh, S-Z., and DiNardo, G. 2011. Modelling the impacts of environmental variation on the distribution of blue marlin, Makaira nigricans, in the Pacific Ocean. – ICES Journal of Marine Science, 68: 1072–1080. Blue marlin are distributed throughout tropical and temperate waters in the Pacific Ocean. The preference of this species for particular habitats may affect its distribution and vulnerability to being caught. The relationships between the spatial pattern of blue marlin abundance and oceanographic conditions, which may be influenced by climate change, were examined using generalized additive models fitted to catch and effort data from longline fisheries. Distributions of blue marlin density, based on combining the probability of presence and abundance given presence, indicate that there is annual variation in the distribution of blue marlin and that the population apparently moved east during the 1997–1998 El Niño. The interannual variability in blue marlin distribution appears to be associated with El Niño events and is related to shifts in sea surface temperature and the deepening of the thermocline. Models of catch and effort that include oceanographic variables could be used, given predictions from climate models, to explore future changes in distribution, which could then be used to provide management advice related to time-area closures.

Tropospheric Planetary Wave Dynamics and Mixture Modeling: Two Preferred Regimes and a Regime Shift

AbstractInvestigation of preferred structures of planetary wave dynamics is addressed using multivariate Gaussian mixture models. The number of components in the mixture is obtained using order statistics of the mixing proportions, hence avoiding previous difficulties related to sample sizes and independence issues. The method is first applied to a few low-order stochastic dynamical systems and data from a general circulation model. The method is next applied to winter daily 500-hPa heights from 1949 to 2003 over the Northern Hemisphere. A spatial clustering algorithm is first applied to the leading two principal components (PCs) and shows significant clustering. The clustering is particularly robust for the first half of the record and less for the second half. The mixture model is then used to identify the clusters. Two highly significant extratropical planetary-scale preferred structures are obtained within the first two to four EOF state space. The first pattern shows a Pacific–North American (PNA) pattern and a negative North Atlantic Oscillation (NAO), and the second pattern is nearly opposite to the first one. It is also observed that some subspaces show multivariate Gaussianity, compatible with linearity, whereas others show multivariate non-Gaussianity. The same analysis is also applied to two subperiods, before and after 1978, and shows a similar regime behavior, with a slight stronger support for the first subperiod. In addition a significant regime shift is also observed between the two periods as well as a change in the shape of the distribution. The patterns associated with the regime shifts reflect essentially a PNA pattern and an NAO pattern consistent with the observed global warming effect on climate and the observed shift in sea surface temperature around the mid-1970s.

Long-term trends and regime shifts in sea surface temperature on the continental shelf of the northeast United States

We investigated sea surface temperature (SST) variability over large spatial and temporal scales for the continental shelf region located off the northeast coast of the United States between Cape Hatteras, North Carolina, and the Gulf of Maine using the extended reconstruction sea surface temperature (ERSST) dataset. The ERSST dataset consists of 2°×2° (latitude and longitude) monthly mean values computed from in situ data derived from the International Comprehensive Ocean Atmosphere Data Set (ICOADS). Nineteen 2°×2° bins were chosen that cover the shelf region of interest between the years of 1854 and 2005. Mean annual and range of SST were examined using dynamic factor analysis to estimate trends in both parameters, while chronological clustering was used to determine temporal SST patterns and breakpoints in the time series that are believed to signal regime shifts in SST. Both SST and SST trend analysis show that interannual variability of SST fluctuations shows strong coherence between bins, with declining SST at the beginning of the last century, followed by increasing SST through 1950, and then rapidly decreasing between 1950 and mid-1960s, with somewhat warmer SST thereafter to present. Annual SST range decreases in a seaward direction for all bins, with strong coherence for interannual variability of range fluctuations between bins. The trend in SST range shows a decreasing range at the beginning of the last century followed by an increase in range from 1920 to the late-1980s, remaining high through present with some spatial variability. A more detailed spatial analysis was conducted by grouping the data into 7 regions using principal component analysis. We analyzed regional trends in mean annual SST, seasonal SST range (summer SST−winter SST), and normalized SST minima and maxima. Both the summer and winter seasons were also analyzed using the length of each season and amplitude of the warming and cooling season, respectively, along with the spring warming and fall cooling rates. Trends in all of the parameters were examined after low-pass filtering using a 10-point convolution filter ( n=10 years) and regime shifts were identified using the sequential t-test analysis of regime shifts (STARS) method. The analysis shows some difference between regions in the timing of minimum SST with minima being reached 1 month earlier in the south (February) relative to more northern regions (March). Regional annual SST range decreased in a seaward direction. Amplitude of summer warming and the length of summer have shown fluctuations with recent years showing stronger warming and longer summers but generally not exceeding past levels. Overall, the difference in SST range, with recent larger values may be the most significant finding of this work. SST range changes have the potential to disrupt species important to local fisheries due to combinations of differing temperature tolerances, changes in reproduction potential, and changes in the distributional range of species.

A global climate model study of CH4 emissions during the Holocene and glacial‐interglacial transitions constrained by ice core data

Ice core records show atmospheric methane mixing ratio and interpolar gradient varying with climate. Changes in wetland sources have been implicated as the basis for this observed variation in the record, but more recently, modeling studies suggest that changes in the CH4 sink resulting from changes in sea surface temperature (SST) and emissions of other volatile organic carbon (VOC) compounds by vegetation must also be considered. We use the Goddard Institute for Space Studies (GISS) General Circulation Model (GCM) with the GISS Tropospheric Chemistry Model to study the response of the methane mixing ratio to source changes during the Holocene and also to a changing chemical sink during glacial‐interglacial transitions. We combine model results with ice core data to demonstrate a method that provides constraints on changes in northern and tropical methane sources. Results show that within the Holocene, changes in the atmospheric methane mixing ratio and latitudinal gradient are not linear with respect to changing methane emissions. Tropical and northern emissions varied from preindustrial levels by as much as 38% and 15%, respectively, within the Holocene. At glacial‐interglacial transitions the methane mixing ratio is sensitive to changes in both VOC and tropical methane emissions and the sensitivity also depends strongly on the assumed SST shift. Our findings suggest that changes in the ice core methane record are likely the result of changes in both the source and the sink. Changes in the sink become especially important when changes in methane mixing ratio and/or climate are large.

Does the differential cost of sons and daughters lead to sex ratio adjustment in great frigatebirds Fregataminor?

Sex allocation theory predicts that if benefits of producing sons and daughters differ and outweigh the costs of sex ratio adjustment, parents should produce more of the offspring that provide them with greater fitness. Potential benefits may be more likely to outweigh costs where sexual size dimorphism and, in birds, single‐egg clutches exist. Great frigatebirds Fregataminor are seabirds in which females are larger than males and clutch size is one egg. In our study population, sexual size dimorphism develops primarily during the period of complete juvenile dependence on parental care, consistent with a higher cost of producing daughters than sons. Over the course of the 1998 breeding season there was a shift from early season prevalence of daughters to late‐season prevalence of sons. Variation in food availability at time of egg laying, as indexed by sea surface temperature (SST), was a strong predictor of offspring sex in 1998. In contrast, SST in 2003 was not a predictor of offspring sex, nor was there a seasonal shift in the hatching sex ratio, despite a seasonal shift in SST. Besides food availability, we tested two additional factors in 2003 that could explain sex ratio adjustment in relation to the cost of reproduction. Offspring sex in 2003 was not related to natural or experimentally induced variation in maternal body condition; pre‐laying food supplements raised the body condition of females at the time of egg laying but did not affect offspring sex or egg mass. In addition, offspring sex was not predicted by the length of maternal telomere restriction fragments (TRFs), an index of age and possibly of reproductive experience. Broad confidence intervals on effect size suggest that undetected effects of maternal condition on offspring sex ratio could easily exist, but confidence intervals were narrower on the non‐significant effects of SST and TRF length on offspring sex ratio. The cause of different seasonal patterns of hatching sex ratio and different SST effects in 1998 and 2003 is unclear.