Ocean Temperature Trends Research Articles

The Transient Response of the Southern Ocean to Stratospheric Ozone Depletion

Abstract Recent studies have suggested that the response of the Southern Ocean to stratospheric ozone depletion is nonmonotonic in time; consisting of an initial cooling followed by a long-term warming. This result may be significant for the attribution of observed Southern Ocean temperature and sea ice trends, but the time scale and magnitude of the response is poorly constrained, with a wide spread among climate models. Furthermore, a long-lived initial cooling period has only been observed in a model with idealized geometry and lacking an explicit representation of ozone. Here the authors calculate the transient response of the Southern Ocean to a step-change in ozone in a comprehensive coupled climate model, GFDL-ESM2Mc. The Southern Ocean responds to ozone depletion with an initial cooling, lasting 25 yr, followed by a warming. The authors extend previous studies to investigate the dependence of the response on the ozone forcing as well as the regional pattern of this response. The response of the Southern Ocean relative to natural variability is shown to be largely independent of the initial state. However, the magnitude of this response is much less than that of natural variability found in the model, which limits its influence and detectability.

A Century of Ocean Warming on Florida Keys Coral Reefs: Historic In Situ Observations

There is strong evidence that global climate change over the last several decades has caused shifts in species distributions, species extinctions, and alterations in the functioning of ecosystems. However, because of high variability on short (i.e., diurnal, seasonal, and annual) timescales as well as the recency of a comprehensive instrumental record, it is difficult to detect or provide evidence for long-term, site-specific trends in ocean temperature. Here we analyze five in situ datasets from Florida Keys coral reef habitats, including historic measurements taken by lighthouse keepers, to provide three independent lines of evidence supporting approximately 0.8 °C of warming in sea surface temperature (SST) over the last century. Results indicate that the warming observed in the records between 1878 and 2012 can be fully accounted for by the warming observed in recent decades (from 1975 to 2007), documented using in situ thermographs on a mid-shore patch reef. The magnitude of warming revealed here is similar to that found in other SST datasets from the region and to that observed in global mean surface temperature. The geologic context and significance of recent ocean warming to coral growth and population dynamics are discussed, as is the future prognosis for the Florida reef tract.

Well-estimated global surface warming in climate projections selected for ENSO phase

The current slowdown in global warming has raised questions about the accuracy of climate model projections. This work selects models that are largely in phase with the natural variability, in this case the El Nino/Southern Oscillation, of the climate system. The selected models are able to predict the recent Pacific Ocean temperature and spatial trends.

Identification of global marine hotspots: sentinels for change and vanguards for adaptation action

Major changes consistent with the fingerprint of global warming have been reported for nearly every ecosystem on earth. Recently, studies have moved beyond correlation-based inference to demonstrate mechanistic links between warming and biological responses, particularly in regions experiencing rapid change. However, the assessment of climate change impacts and development of adaptation options that humans can undertake are at the earliest stages, particularly for marine systems. Here, we use trends in ocean temperature to characterize regions that can act as natural laboratories or focal points for early learning. These discrete marine ‘hotspots’, where ocean warming is fastest, were identified based on 50 years of historical sea surface temperature data. Persistence of these hotspots into the future was evaluated using global climate models. This analysis provides insights and a starting point for scientists aiming to identify key regions of concern with regard to ocean warming, and illustrates a potential approach for considering additional physical drivers of change such as ocean pH or oxygenation. We found that some hotspot regions were of particular concern due to other non-climate stressors. For instance, many of the marine hotspots occur where human dependence on marine resources is greatest, such as south-east Asia and western Africa, and are therefore of critical consideration in the context of food security. Intensive study and development of comprehensive inter-disciplinary networks based on the hotspot regions identified here will allow earliest testing of management and adaptation pathways, facilitating rapid global learning and implementation of adaptation options to cope with future change.

A Dynamic, Coupled Thermal Reservoir Approach to Atmospheric Energy Transfer Part Ii: Applications

The coupled thermal reservoir approach described in Part I is demonstrated by analyzing flux and meteorological data covering a range of thermal reservoir conditions. These include mid latitude ocean thermal storage, the surface flux balance of the Pacific warm pool and the land surface flux balance in S. California. In addition to temperature data, the effects of thermal gradients, flux interaction lengths and the time delay or phase shift between the heating flux and the temperature response are considered. Long term climate trends in weather station minimum meteorological surface air temperature (MSAT) data are also analyzed. For selected California and UK weather stations these follow the regional trends in ocean surface temperature. This allows urban heat island effects and other weather station biases to be investigated. The effect of a 100 ppm increase in atmospheric CO2 concentration on these data sets is shown to be too small to be measured.

Recent sea level and upper ocean temperature variability and trends; cook islands regional results and perspective

The goal of this paper is to provide information on the sea level and upper ocean temperature variability and trends in the Cook Islands region within a global context. Oceanic fisheries variability and change take place within the physical environment. Because the state of the historical data set is not as would be desired, we begin with some review of data distribution issues. We provide some new results from the Cook Islands region but draw upon previous work for information about the global and ocean-basin scale context. There are clear trends over recent decades in sea level and, generally, in upper ocean temperature, but there is also substantial interannual and interdecadal variability, which are larger locally than globally. Because of this variability, it is not possible to say if recent Cook Islands regional trends are representative of longer-term trends, or if longer-term trends have increased recently. Trends in the Cook Islands region over the last four decades are ~0.1–0.3 °C per decade in near surface temperature and ~2–3 cm sea level per decade.

Reconciling disparate twentieth-century Indo-Pacific ocean temperature trends in the instrumental record

Accurately characterizing natural versus forced sea surface temperature variability in observations is needed to validate and verify climate models used for projections of future climate change. This study successfully resolves previous large discrepancies in estimated tropical Indo-Pacific twentieth-century trends between observationally based sea surface temperature reconstructions.

Variability in the ICES/NAFO region between 1950 and 2009: observations from the ICES Report on Ocean Climate

Abstract Hughes, S. L., Holliday, N. P., Gaillard, F., and the ICES Working Group on Oceanic Hydrography, 2012. Variability in the ICES/NAFO region between 1950 and 2009: observations from the ICES Report on Ocean Climate. – ICES Journal of Marine Science, 69: 706–719. The ICES Report on Ocean Climate presents the latest information on the status and trends of sea temperature and salinity in the North Atlantic and Nordic Seas. It is the main product of the ICES Working Group on Oceanic Hydrography, published annually. Bringing together multiple time-series from across the ICES and NAFO regions offers insight into the concurrent spatial and temporal trends in ocean temperature and salinity. This paper presents an overview of the physical variability in the North Atlantic Ocean at decadal and longer time-scales and reviews the current state of understanding of the causes and mechanisms of this variability. Between the 1960s and the 1990s, the North Atlantic Oscillation (NAO) index increased from a persistent negative phase in the 1960s to a strong positive phase during the 1980s and early 1990s. However, during the decade 2000–2009, because of shifts in atmospheric pressure patterns, the NAO was weak and the NAO index was not a good indicator of atmospheric forcing. Marked changes were also observed in oceanographic indices such as the Subpolar Gyre index during the mid-1990s and, as a consequence, conditions in the decade 2000–2009 have been very different from those of the previous four decades.

Late Cretaceous–Neogene trends in deep ocean temperature and continental ice volume: Reconciling records of benthic foraminiferal geochemistry (δ18O and Mg/Ca) with sea level history

[1] We reconstruct trends in ice volume and deep ocean temperature for the past 108 Myr, resolving variations on timescales of ∼2 Myr and longer. We use a sea level record as a proxy for ice volume, a benthic foraminiferal Mg/Cabf record as a proxy for temperature, and a benthic foraminiferal δ18Obf record as a proxy for both. This allows us to construct dual estimates of temperature and ice volume variations for the interval 10–60 Ma: extracting temperature from δ18Obf by using sea level as a proxy for ice volume to constrain the δ18Osw component, and extracting seawater δ18Osw (which reflects ice volume) from δ18Obf by using Mg/Cabf to constrain the temperature component. Each of these approaches requires numerous assumptions, but the range of plausible solutions are concordant on timescales >2 Myr and within an uncertainty of ±2°C temperature and ±0.4‰ δ18Osw. The agreement between the two approaches for the last 50 Myr provides empirical justification for the use of δ18Obf, Mg/Cabf, and sea level records as robust climate proxies. Our reconstructions indicate differences between deep ocean cooling and continental ice growth in the late Cenozoic: cooling occurred gradually in the middle–late Eocene and late Miocene–Pliocene while ice growth occurred rapidly in the earliest Oligocene, middle Miocene, and Plio-Pleistocene. These differences are consistent with climate models that imply that temperatures, set by the long-term CO2 equilibrium, should change only gradually on timescales >2 Myr, but growth of continental ice sheets may be rapid in response to climate thresholds due to feedbacks that are not yet fully understood.

Coupled high-resolution marine and terrestrial records of carbon and hydrologic cycles variations during the Paleocene–Eocene Thermal Maximum (PETM)

The Paleocene–Eocene Thermal Maximum is characterized by a massive perturbation of the global carbon cycle reflected in a large, negative carbon isotope excursion associated with rapid global warming and changes in the hydrologic system. The magnitude of the carbon isotope excursion from terrestrial carbonates and organic carbon is generally larger relative to marine carbonates. However, high-resolution marine and terrestrial isotopic records from the same locality for direct comparison are limited. Here we present coupled carbon isotope records from terrestrial biomarkers (δ 13C n-alkane ), marine bulk carbonates (δ 13C carbonate), and bulk organic carbon (δ 13C organic) from the continuous sedimentary record of the Forada section in northern Italy in order to evaluate the magnitude and phase relationships between terrestrial and marine environments. Consistent with previous reports, we find that the carbon isotope excursion established from δ 13C n-alkane values is more negative than those established from δ 13C carbonate and δ 13C organic values. In contrast to the majority of PETM records, all Forada δ 13C records show a sharp 13C-enrichment immediately following the onset of the carbon isotope excursion. Further, the terrestrial δ 13C n-alkane record lags δ 13C carbonate/δ 13C organic trends by ~ 4–5 kyr—offsets that reflect the long residence time of soil organic carbon. Hydrogen isotope records from higher-plant leaf waxes (δD n-alkane ) and sea-surface temperatures (TEX 86) were established to assess hydrologic and ocean temperature trends. We find δD n-alkane values trend more positive, associated with higher temperatures prior to the onset of the carbon isotope excursion, and conclude that regional changes in the hydrologic cycle likely occurred before the onset of the carbon isotope anomaly.

Decadal predictability of tropical Indo-Pacific Ocean temperature trends due to anthropogenic forcing in a coupled climate model

[1] This study quantifies the impact of ENSO on the decadal predictability of tropical Indo‐Pacific Ocean trends in a very large ensemble of NCAR CCSM3 anthropogenically‐forced (A1B scenario) simulations, by decomposing upper ocean temperatures into “ENSO” and “non‐ENSO” variability. On decadal time scales, the ENSO pattern primarily contributes totheensemblespreadandhasatrendwhoseamplitudeisnot predictable.However,the non‐ENSOcomponentofthetrend has much smaller spread and is predictable after 10 years, much sooner than the total trend, which is predictable after 25 years. The non‐ENSO component of the trend explains 96% of the total trend and has a structure that is distinct from ENSO, including cooling in the South Pacific due to increased southeast trades, warming of the warm pool, and strengthening of the equatorial Pacific near‐surface temperature gradient superimposedupon a uniform warming. Citation: Solomon, A., and M. Newman (2011), Decadal predictability of tropical Indo‐Pacific Ocean temperature trends due to anthropogenic forcing in a coupled climate model, Geophys. Res. Lett., 38, L02703, doi:10.1029/2010GL045978.

Warming of Global Abyssal and Deep Southern Ocean Waters between the 1990s and 2000s: Contributions to Global Heat and Sea Level Rise Budgets*

Abstract Abyssal global and deep Southern Ocean temperature trends are quantified between the 1990s and 2000s to assess the role of recent warming of these regions in global heat and sea level budgets. The authors 1) compute warming rates with uncertainties along 28 full-depth, high-quality hydrographic sections that have been occupied two or more times between 1980 and 2010; 2) divide the global ocean into 32 basins, defined by the topography and climatological ocean bottom temperatures; and then 3) estimate temperature trends in the 24 sampled basins. The three southernmost basins show a strong statistically significant abyssal warming trend, with that warming signal weakening to the north in the central Pacific, western Atlantic, and eastern Indian Oceans. Eastern Atlantic and western Indian Ocean basins show statistically insignificant abyssal cooling trends. Excepting the Arctic Ocean and Nordic seas, the rate of abyssal (below 4000 m) global ocean heat content change in the 1990s and 2000s is equivalent to a heat flux of 0.027 (±0.009) W m−2 applied over the entire surface of the earth. Deep (1000–4000 m) warming south of the Subantarctic Front of the Antarctic Circumpolar Current adds 0.068 (±0.062) W m−2. The abyssal warming produces a 0.053 (±0.017) mm yr−1 increase in global average sea level and the deep warming south of the Subantarctic Front adds another 0.093 (±0.081) mm yr−1. Thus, warming in these regions, ventilated primarily by Antarctic Bottom Water, accounts for a statistically significant fraction of the present global energy and sea level budgets.

Divergent trends in land and ocean temperature in the Southern Ocean over the past 18,000 years

Reconstructions of land and ocean temperatures over the past 18,000 years in the high southern latitudes have shown conflicting trends. Analyses of temperatures on Campbell Island, south of New Zealand, confirm this behaviour, and lead to the suggestion that it reflects changes in the position and intensity of the westerly winds. Over the past 18,000 years, sea surface temperatures for the Southern Ocean do not align with those of the adjacent, high-latitude landmasses. During the late glacial period, the ocean surface warmed rapidly to present-day temperatures1, whereas the land warmed only slowly, as evidenced by the lagged response of forest and glaciers2,3. However, in the Holocene epoch, land-based records suggest strong warming whereas marine records indicate that ocean surface temperatures cooled. Here we present reconstructions of summer temperature for Campbell Island, in the Southern Ocean, over the past 16,500 years based on fossil pollen. We find a pronounced warming 12,500–11,000 years ago, a cooling until 9,200 years ago, and a rapid warming to a peak between 6,000 and 5,000 years ago, followed by minor cool intervals from 5,200–4,000, 3,000–1,700 and 700–100 years ago. As expected, our temperature reconstructions show a late glacial lag behind nearby records of sea surface temperature6,7, and opposing trends in the Holocene. We suggest that this discrepancy arises because land-based reconstructions record summer temperatures, whereas marine proxies generally reflect annual temperatures. We conclude that the divergence of the records therefore reflects changes in the seasonality of atmospheric heat transport. As atmospheric heat transport is tied to the Southern Hemisphere westerly winds, we attribute our observed changes to shifts in the position and intensity of the southern westerlies.

Long-Term Sea Surface Temperature Variability along the U.S. East Coast

Abstract Sea surface temperature variations along the entire U.S. East Coast from 1875 to 2007 are characterized using a collection of historical observations from lighthouses and lightships combined with recent buoy and shore-based measurements. Long-term coastal temperature trends are warming in the Gulf of Maine [1.0° ± 0.3°C (100 yr)−1] and Middle Atlantic Bight [0.7° ± 0.3°C (100 yr)−1], whereas trends are weakly cooling or not significant in the South Atlantic Bight [−0.1° ± 0.3°C (100 yr)−1] and off Florida [−0.3° ± 0.2°C (100 yr)−1]. Over the last century, temperatures along the northeastern U.S. coast have warmed at a rate 1.8–2.5 times the regional atmospheric temperature trend but are comparable to warming rates for the Arctic and Labrador, the source of coastal ocean waters north of Cape Hatteras (36°N). South of Cape Hatteras, coastal ocean temperature trends match the regional atmospheric temperature trend. The observations and a simple model show that along-shelf transport, associated with the mean coastal current system running from Labrador to Cape Hatteras, is the mechanism controlling long-term temperature changes for this region and not the local air–sea exchange of heat.

The observed and simulated anatomy of ocean temperature trends

This article was submitted without an abstract, please refer to the full-text PDF file.

Is the Upper Ocean Warming? Comparisons of 50-Year Trends from Different Analyses*

Abstract There is great interest in World Ocean temperature trends, yet the historical global ocean database has very uneven coverage in space and time. Previous work on 50-yr upper ocean temperature trends from the NOAA ocean data archive is extended here. Trends at depths from 50 to 1000 m are examined, based on observations gridded over larger regions than in the earlier study. Despite the use of larger grid boxes, most of the ocean does not have significant 50-yr trends at the 90% confidence level (CL). In fact only 30% of the ocean at 50 m has 90% CL trends, and the percentage decreases significantly with increasing depth. As noted in the previous study, there is much spatial structure in 50-yr trends, with areas of strong warming and strong cooling. These trend results are compared with trends calculated from data interpolated to standard levels and from a highly horizontally interpolated version of the dataset that has been used in previous heat content trend studies. The regional trend results can differ substantially, even in the areas with statistically significant trends. Trends based on the more interpolated analyses show more warming. Together with major temporal and spatial sampling limitations, the previously described strong interdecadal and spatial variability of trends makes it very difficult to formally estimate uncertainty in World Ocean averages, but these results suggest that upper ocean heat content integrals and integral trends may be substantially more uncertain than has yet been acknowledged. Further exploration of uncertainties is needed.

Sensitivity of global warming to the pattern of tropical ocean warming

The current generations of climate models are in substantial disagreement as to the projected patterns of sea surface temperatures (SSTs) in the Tropics over the next several decades. We show that the spatial patterns of tropical ocean temperature trends have a strong influence on global mean temperature and precipitation and on global mean radiative forcing. We identify the SST patterns with the greatest influence on the global mean climate and find very different, and often opposing, sensitivities to SST changes in the tropical Indian and West Pacific Oceans. Our work stresses the need to reduce climate model biases in these sensitive regions, as they not only affect the regional climates of the nearby densely populated continents, but also have a disproportionately large effect on the global climate.

Secular trends and climate drift in coupled ocean‐atmosphere general circulation models

Coupled ocean‐atmosphere general circulation models (coupled GCMs) with interactive sea ice are the primary tool for investigating possible future global warming and numerous other issues in climate science. A long‐standing problem with such models is that when different components of the physical climate system are linked together, the simulated climate can drift away from observation unless constrained by ad hoc adjustments to interface fluxes. However, 11 modern coupled GCMs, including three that do not employ flux adjustments, behave much better in this respect than the older generation of models. Surface temperature trends in control run simulations (with external climate forcing such as solar brightness and atmospheric carbon dioxide held constant) are small compared with observed trends, which include 20th century climate change due to both anthropogenic and natural factors. Sea ice changes in the models are dominated by interannual variations. Deep ocean temperature and salinity trends are small enough for model control runs to extend over 1000 simulated years or more, but trends in some regions, most notably the Arctic, differ substantially among the models and may be problematic. Methods used to initialize coupled GCMs can mitigate climate drift but cannot eliminate it. Lengthy “spin‐ups” of models, made possible by increasing computer power, are one reason for the improvements this paper documents.

Temperature Trend of the Last 40 Yr in the Upper Pacific Ocean

The linear temperature trend of the last 40 yr (1955–94) in the upper Pacific Ocean above 400 m is studied using an objectively analyzed dataset and simulations of an ocean general circulation model. Both the data and simulations suggest a warming trend in the western tropical Pacific (10°S–10°N) near the surface and in the eastern tropical Pacific above 400 m but a cooling trend in the thermocline of the western tropical Pacific. In the midlatitude North Pacific (30°–50°N), the temperature trend is positive east of 150°W but negative to the west. Simulated heat budget indicates that the temperature trend in the tropical Pacific may result from oceanic advection. In the central and western Pacific, the surface warming is associated with the reduction of cold advection from the off-equatorial divergent flow and the South Equatorial Current, while the cooling in the thermocline is related to the reduction of equatorward warm advection. In the eastern Pacific, the warming is associated with the reduction of upwelling. The reduction of these ocean currents, in turn, may result largely from the weakening of the trade winds. In the midlatitude North Pacific, the ocean temperature trends similarly may result from the oceanic advection associated with the reduction of the westerlies. The effect of net surface heat flux into the ocean is a damping factor to the sea surface temperature. These studies highlight the importance of oceanic advection in producing long-term temperature trends.

LONG‐TERM VARIABILITY IN THE LOW‐LEVEL INVERSION LAYER OVER THE ARCTIC OCEAN

Long-term changes in the low-level tropospheric inversion layer are investigated using nearly 30 000 Arctic Ocean temperature profiles for 1950–1990. The profile measurements were made by radiosonde at the former USSR ‘North Pole’ series of drifting ice stations, and by dropsonde from US Air Force ‘Ptarmigan’ weather reconnaissance aircraft. Significant increases in the temperature difference across the inversion layer are found during winter and autumn, indicating a strengthening of the thermal stability of the layer. This strengthening is in agreement with a recent study describing Arctic Ocean temperature trends, but is in contrast to general circulation model predictions of polar amplification of greenhouse-induced warming. The frequency with which inversion layers occur has increased, with inversions tending to be more elevated above the ice surface. Decreases in inversion layer depth reported by other investigations using similar sounding data sets are not confirmed.