Global Ocean Temperature Research Articles

Local and global climatic drivers of Atlantic salmon decline in southern Europe

The abundance of Atlantic salmon is declining throughout its geographical area. Fisheries and global warming were assumed as main drivers of the decline, and recent studies suggest that habitat changes in freshwater is a third contributor. Southern populations experience the greatest decline, and face the highest risk of extinction as global warming moves its thermal niche northwards. We analysed long-term catch data (1949–2013) from a salmon fishery in northern Spain, and examined its relationship with local and global indicators of temperature and hydrological change. CPUE data, analysed by ARIMA time-series models, exhibited a significant negative trend and a marked decrease since 1973–1974, possibly triggered by overfishing at sea and a sudden outbreak of disease. Temperature increased in the same period, particularly so since 1986–1988, being negatively correlated with CPUE. A significant change in magnitude and duration of extreme water conditions occurred from 1970s onwards. Indicators of hydrological shift were also significantly correlated with CPUE of returning salmon. The best ARIMAX models indicated however, that the decrease in salmon CPUE was mainly driven by temperature trends. This indicates that both local (temperature and flow in the river) and global (ocean temperature) factors have contributed to the decrease in salmon numbers, and that temperature has played the major role. Despite a strong reduction in fishing pressure after the 1970s widespread collapse, our study population did not recover to previous abundance levels. This suggests the operation of additional factors, being climate warming and changes in food webs of the North Atlantic the most likely reasons.

Biotic impacts of temperature before, during, and after the end-Permian extinction: A multi-metric and multi-scale approach to modeling extinction and recovery dynamics

Extinction and delayed recovery during the end-Permian extinction and Early Triassic has been linked to environmental instability brought on by volcanic outgassing and greenhouse conditions, but the relative importance of the myriad of environmental stressors at this time on recovery dynamics is not well understood. Previous workers have documented both overall delayed biotic recovery for the entirety of the Early Triassic, but also incipient recoveries that appear to occur relatively early after the initial extinction event. Here, we explore the patterns of extinction and recovery using several metrics of ecological complexity in marine benthic communities using a global dataset, and compare several multiple regression models to determine which set of abiotic factors best predicts extinction and recovery dynamics. We additionally test the importance of temporal scale of analysis in interpretations of recovery dynamics and modeling results, by including analyses at the epoch, stage, and substage scales bracketing the interval of extinction and recovery. We find differences in mode of recovery between the ecological metrics analyzed, with some metrics exhibiting an Early Triassic recovery lag, while others recover continuously or immediately following the initial extinction event. We also find evidence of a global ‘Dienerian minimum’, with overall levels of community complexity significantly lower than earlier Griesbachian communities, suggesting a synchronous disturbance to the progression of recovery at this time. The regression model with δ18Oapatite mean values as the response variable is most often found to be the best-fit model across all time scales analyzed, though proxies of rock record fidelity and paleontological sampling effort become more important in finer timescale analyses, likely due to dwindling sample numbers. Out of the models tested, these results suggest that global ocean temperatures best predict patterns of extinction and recovery across several ecological metrics, and that thermal episodes during the initial extinction event and subsequently in the Early Triassic recovery period significantly suppressed benthic marine community health.

Trends in summer bottom-water temperatures on the northern Gulf of Mexico continental shelf from 1985 to 2015

We quantified trends in the 1985 to 2015 summer bottom-water temperature on the northern Gulf of Mexico (nGOM) continental shelf for data collected at 88 stations with depths ranging from 3 to 63 m. The analysis was supplemented with monthly data collected from 1963 to 1965 in the same area. The seasonal summer peak in average bottom-water temperature varied concurrently with air temperature, but with a 2- to 5-month lag. The summer bottom-water temperature declined gradually with depth from 30 oC at stations closest to the shore, to 20 oC at the offshore edge of the study area, and increased an average 0.051 oC y-1 between1963 and 2015. The bottom-water warming in summer for all stations was 1.9 times faster compared to the rise in local summer air temperatures, and 6.4 times faster than the concurrent increase in annual global ocean sea surface temperatures. The annual rise in average summer bottom-water temperatures on the subtropical nGOM continental shelf is comparable to the few published temperature trend estimates from colder environments. These recent changes in the heat storage on the nGOM continental shelf will affect oxygen and carbon cycling, spatial distribution of fish and shrimp, and overall species diversity.

Assessing the ecosystem-level consequences of a small-scale artisanal kelp fishery within the context of climate-change.

Coastal communities worldwide rely on small-scale artisanal fisheries as a means of increasing food security and alleviating poverty. Even small-scale fishing activities, however, are prone to resource depletion and environmental degradation, which can erode livelihoods in the long run. Thus, there is a pressing need to identify viable and resilient artisanal fisheries, and generate knowledge to support management within the context of a rapidly changing climate. We examined the ecosystem-level consequences of an artisanal kelp fishery (Macrocystis pyrifera), finding small-scale harvest of this highly productive species poses minimal impacts on kelp recovery rates, survival, and biomass dynamics, and abundances of associated commercial and culturally important fish species. These results suggest that small-scale harvest poses minimal trade-offs for the other economic benefits provided by these ecosystems, and their inherent, spiritual, and cultural value to humans. However, we detected a negative impact of warmer seawater temperatures on kelp recovery rates following harvest, indicating that the viability of harvest, even at small scales, may be threatened by future increases in global ocean temperature. This suggests that negative impacts of artisanal fisheries may be more likely to arise in the context of a warming climate, further highlighting the widespread effects of global climate change on coastal fisheries and livelihoods.

Global and Full-Depth Ocean Temperature Trends during the Early Twenty-First Century from Argo and Repeat Hydrography

The early twenty-first century’s warming trend of the full-depth global ocean is calculated by combining the analysis of Argo (top 2000 m) and repeat hydrography into a blended full-depth observing system. The surface-to-bottom temperature change over the last decade of sustained observation is equivalent to a heat uptake of 0.71 ± 0.09 W m−2 applied over the surface of Earth, 90% of it being found above 2000-m depth. The authors decompose the temperature trend pointwise into changes in isopycnal depth (heave) and temperature changes along an isopycnal (spiciness) to describe the mechanisms controlling the variability. The heave component dominates the global heat content increase, with the largest trends found in the Southern Hemisphere’s extratropics (0–2000 m) highlighting a volumetric increase of subtropical mode waters. Significant heave-related warming is also found in the deep North Atlantic and Southern Oceans (2000–4000 m), reflecting a potential decrease in deep water mass renewal rates. The spiciness component shows its strongest contribution at intermediate levels (700–2000 m), with striking localized warming signals in regions of intense vertical mixing (North Atlantic and Southern Oceans). Finally, the agreement between the independent Argo and repeat hydrography temperature changes at 2000 m provides an overall good confidence in the blended heat content evaluation on global and ocean scales but also highlights basin-scale discrepancies between the two independent estimates. Those mismatches are largest in those basins with the largest heave signature (Southern Ocean) and reflect both the temporal and spatial sparseness of the hydrography sampling.

Impact of the GeoMIP G1 sunshade geoengineering experiment on the Atlantic meridional overturning circulation

We analyze the multi-earth system model responses of ocean temperatures and the Atlantic Meridional Overturning Circulation (AMOC) under an idealized solar radiation management scenario (G1) from the Geoengineering Model Intercomparison Project. All models simulate warming of the northern North Atlantic relative to no geoengineering, despite geoengineering substantially offsetting the increases in mean global ocean temperatures. Increases in the temperature of the North Atlantic Ocean at the surface (∼0.25 K) and at a depth of 500 m (∼0.10 K) are mainly due to a 10 Wm−2 reduction of total heat flux from ocean to atmosphere. Although the AMOC is slightly reduced under the solar dimming scenario, G1, relative to piControl, it is about 37% stronger than under abrupt4 × CO2. The reduction of the AMOC under G1 is mainly a response to the heat flux change at the northern North Atlantic rather than to changes in the water flux and the wind stress. The AMOC transfers heat from tropics to high latitudes, helping to warm the high latitudes, and its strength is maintained under solar dimming rather than weakened by greenhouse gas forcing acting alone. Hence the relative reduction in high latitude ocean temperatures provided by solar radiation geoengineering, would tend to be counteracted by the correspondingly active AMOC circulation which furthermore transports warm surface waters towards the Greenland ice sheet, warming Arctic sea ice and permafrost.

LiDAR remote sensing of the cryosphere: Present applications and future prospects

The cryosphere consists of frozen water and includes lakes/rivers/sea ice, glaciers, ice caps/sheets, snow cover, and permafrost. Because highly reflective snow and ice are the main components of the cryosphere, it plays an important role in the global energy balance. Thus, any qualitative or quantitative change in the physical properties and extents of the cryosphere affects global air circulation, ocean and air temperatures, sea level, and ocean current patterns. Due to the hardships involved in collecting ground control points and field data for high alpine glaciers or vast polar ice sheets, several researchers are currently using remote sensing. Satellites provide an effective space-borne platform for remotely sensing frozen areas at the global and regional scales. However, satellite remote sensing has several constraints, such as limited spatial and temporal resolutions and expensive data acquisition. Therefore, aerial and terrestrial remote sensing platforms and sensors are needed to cover temporal and spatial gaps for comprehensive cryospheric research. Light Detection and Ranging (LiDAR) antennas form a group of active remote sensors that can easily be deployed on all three platforms, i.e., satellite, aerial, and terrestrial. The generation of elevation data for glacial and snow-covered terrain from photogrammetry requires high contrast amongst various reflective surfaces (ice, snow, firn, and slush). Conventional passive optical remote sensors do not provide the necessary accuracy, especially due to the unavailability of reliable ground control points. However, active LiDAR sensors can fill this research gap and provide high-resolution and accurate Digital Elevation Models (DEMs). Due to the obvious advantages of LiDAR over conventional passive remote sensors, the number of LiDAR-based cryospheric studies has increased in recent years. In this review, we highlight studies that have utilised LiDAR sensors for the cryospheric research of various features, such as snow cover, polar ice sheets and their atmospheres, alpine glaciers, and permafrost. Because this technology shows immense promise for applications in future cryospheric research, we also emphasise the prospects of utilising LiDAR sensors. In this paper, a large compilation of relevant references is presented to allow readers to explore particular topics of interest.

The impact of observational sampling on time series of global 0–700 m ocean average temperature: a case study

ABSTRACTThe limited historical observational sampling of the ocean gives rise to uncertainty in time series of global ocean temperature anomalies calculated from those observations. Without knowledge of the true global state of the oceans, it is difficult to characterize the errors caused by these sampling issues. One way to quantify them is to use climate model data. Pseudo observational time series can be constructed from the model data using knowledge of where observations occurred. Comparison of these with time series constructed from the full model fields yields information about how observational sampling impacts time series of the temperature change in the modelled world. This can then be related back to the time series generated from the real observations. In this study, climate model data were used to investigate sampling errors in 0–700 m global average ocean temperature anomaly time series calculated using a straightforward gridding approach. The sampling had two impacts. First, sampling causes issues with constructing a climatology that is representative of the long‐term average state of the ocean. Climatology errors were shown to have the potential to cause systematically changing errors in anomaly time series. Second, some regions of the ocean were poorly observed prior to improvements brought about by the Argo project. This was found to cause spurious variability, both year to year and over multi‐year time scales. The latter had similar magnitude to the actual multi‐year variability seen in the model data but was smaller than the model's long‐term temperature change. The features of these errors depend on the ocean state and therefore varied between climate model runs. More sophisticated methods used to calculate ocean temperature time series are expected to be less impacted by sampling. Nevertheless, sampling errors will still occur and therefore this type of study is recommended even for those techniques.

In Situ–Based Reanalysis of the Global Ocean Temperature and Salinity with ISAS: Variability of the Heat Content and Steric Height

Abstract The In Situ Analysis System (ISAS) was developed to produce gridded fields of temperature and salinity that preserve as much as possible the time and space sampling capabilities of the Argo network of profiling floats. Since the first global reanalysis performed in 2009, the system has evolved, and a careful delayed-mode processing of the 2002–12 dataset has been carried out using version 6 of ISAS and updating the statistics to produce the ISAS13 analysis. This last version is now implemented as the operational analysis tool at the Coriolis data center. The robustness of the results with respect to the system evolution is explored through global quantities of climatological interest: the ocean heat content and the steric height. Estimates of errors consistent with the methodology are computed. This study shows that building reliable statistics on the fields is fundamental to improve the monthly estimates and to determine the absolute error bars. The new mean fields and variances deduced from the ISAS13 reanalysis and dataset show significant changes relative to the previous ISAS estimates, in particular in the Southern Ocean, justifying the iterative procedure. During the decade covered by Argo, the intermediate waters appear warmer and saltier in the North Atlantic and fresher in the Southern Ocean than in World Ocean Atlas 2005 long-term mean. At interannual scale, the impact of ENSO on the ocean heat content and steric height is observed during the 2006/07 and 2009/10 events captured by the network.

Enhanced warming of the Northwest Atlantic Ocean under climate change

AbstractThe Intergovernmental Panel on Climate Change (IPCC) fifth assessment of projected global and regional ocean temperature change is based on global climate models that have coarse (∼100 km) ocean and atmosphere resolutions. In the Northwest Atlantic, the ensemble of global climate models has a warm bias in sea surface temperature due to a misrepresentation of the Gulf Stream position; thus, existing climate change projections are based on unrealistic regional ocean circulation. Here we compare simulations and an atmospheric CO2 doubling response from four global climate models of varying ocean and atmosphere resolution. We find that the highest resolution climate model (∼10 km ocean, ∼50 km atmosphere) resolves Northwest Atlantic circulation and water mass distribution most accurately. The CO2 doubling response from this model shows that upper‐ocean (0–300 m) temperature in the Northwest Atlantic Shelf warms at a rate nearly twice as fast as the coarser models and nearly three times faster than the global average. This enhanced warming is accompanied by an increase in salinity due to a change in water mass distribution that is related to a retreat of the Labrador Current and a northerly shift of the Gulf Stream. Both observations and the climate model demonstrate a robust relationship between a weakening Atlantic Meridional Overturning Circulation (AMOC) and an increase in the proportion of Warm‐Temperate Slope Water entering the Northwest Atlantic Shelf. Therefore, prior climate change projections for the Northwest Atlantic may be far too conservative. These results point to the need to improve simulations of basin and regional‐scale ocean circulation.

Eco-physiological adaptation shapes the response of calcifying algae to nutrient limitation.

The steady increase in global ocean temperature will most likely lead to nutrient limitation in the photic zone. This will impact the physiology of marine algae, including the globally important calcifying coccolithophores. Understanding their adaptive patterns is essential for modelling carbon production in a low-nutrient ocean. We investigated the physiology of Helicosphaera carteri, a representative of the abundant but under-investigated flagellated functional group of coccolithophores. Two strains isolated from contrasting nutrient regimes (South Atlantic and Mediterranean Sea) were grown in phosphorus-replete and phosphorus-limited batch cultures. While growing exponentially in a phosphorus-replete medium, the Mediterranean strain exhibited on average 24% lower growth rate, 36% larger coccosphere volume and 21% lower particulate inorganic carbon (PIC) production than the Atlantic strain. Under phosphorus limitation, the same strain was capable of reaching a 2.6 times higher cell density than the Atlantic strain due to lower phosphorus requirements. These results suggest that local physiological adaptation can define the performance of this species under nutrient limitation.

A case study of multi-annual temperature oscillations in the atmosphere: Middle Europe

SABER temperature measurements from 2002 to 2012 are analyzed from 18 to 110km altitude in Middle Europe. Data are complemented by radiosonde measurements in the altitude range from 0 to 30km. Low frequency oscillations with periods of about 2.4–2.2 yr, 3.4 yr, and 5.5 yr are seen in either data set. Surprising vertical structures in amplitudes and phases are observed with alternating minima and maxima of amplitudes, steep phase changes (180°) at the altitudes of the minima, and constant phase values in between. HAMMONIA CCM simulations driven by boundary conditions for the years 1996–2006 are analyzed for corresponding features, and very similar structures are found. Data from another CCM, the CESM-WACCM model, are also analyzed and show comparable results.Similar oscillation periods have been reported in the literature for the ocean. A possible forcing of the atmospheric oscillations from below was therefore tested with a special HAMMONIA run. Here, climatological boundary conditions were used, i.e. the boundaries in all eleven years were the same. Surprisingly also in this data set the same atmospheric oscillations are obtained. We therefore conclude that the oscillations are intrinsically forced, self-sustained in the atmosphere. The oscillations turned out to be quite robust as they are still found in a HAMMONIA run with strongly reduced vertical resolution. Here only the form of the vertical amplitude and phase profile of the 2.2 yr feature is lost but the oscillation itself is still there, and the two other oscillations are essentially unchanged.Similar oscillations are seen in the earth surface temperatures. Global Land Ocean Temperature Index data (GLOTI) reaching back to 1880 show such oscillations during all that time. The oscillations are also seen in parameters other than atmospheric temperature. They are found in surface data such as the North Atlantic Oscillation Index (NAO) and in zonal winds in the troposphere and lower stratosphere. The oscillations found are tentatively discussed in terms (of synchronization) of self-sustained non-linear oscillators, as many of their properties resemble such oscillators described in the literature.

Robust global ocean cooling trend for the pre-industrial Common Era

Knowledge of natural climate variability is essential to better constrain the uncertainties in projections of twenty-first-century climate change 1–5. The past 2,000 years (2 kyr) have emerged as a critical interval in this endeavour, with sufficient length to characterize natural decadal-to-centennial scale change, known external climate forcings 6 and with distinctive patterns of spatiotemporal temperature variations 7. However, reconstructions for the full 2 kyr interval are not available for the global ocean, a primary heat reservoir 8 and an important regulator of global climate on longer timescales 9–11. Here we present a global ocean sea surface temperature (SST) synthesis (Ocean2k SST synthesis) spanning the Common Era, which shows a cooling trend that is similar, within uncertainty, to that simulated by realistically forced climate models for the past millennium. We use the simulations to identify the climate forcing(s) consistent with reconstructed SST variations during the past millennium. The oceans mediate the response of global climate to natural and anthropogenic forcings. Yet for the past 2,000 years — a key interval for understanding the present and future climate response to these forcings — global sea surface temperature changes and the underlying driving mechanisms are poorly constrained. Here we present a global synthesis of sea surface temperatures for the Common Era (ce) derived from 57 individual marine reconstructions that meet strict quality control criteria. We observe a cooling trend from 1 to 1800 ce that is robust against explicit tests for potential biases in the reconstructions. Between 801 and 1800 ce, the surface cooling trend is qualitatively consistent with an independent synthesis of terrestrial temperature reconstructions, and with a sea surface temperature composite derived from an ensemble of climate model simulations using best estimates of past external radiative forcings. Climate simulations using single and cumulative forcings suggest that the ocean surface cooling trend from 801 to 1800 ce is not primarily a response to orbital forcing but arises from a high frequency of explosive volcanism. Our results show that repeated clusters of volcanic eruptions can induce a net negative radiative forcing that results in a centennial and global scale cooling trend via a decline in mixed-layer oceanic heat content.

Melting of Sea Ice Inexplicable for Recent Global Eustatic Sea Level Rise

Global warming and associated sea level rise due to melting of major ice reserves is one of the most important and debated issues of present time. It has unequivocally been proved that mean global surface and ocean temperature is increasing due to anthropogenic input of greenhouse gases like carbon dioxide which has reached its maximum concentration up to 399.35 ppm since last 650,000 years. Due to greenhouse effect global ice caps, sheets and sea ice are melting. But there is an ambiguity of rate of melting of ice and rate of global sea level rise. This can be best exemplified by melting rate of Arctic sea ice with nonequivalent response to the rate of global sea level rise. Conceptual model proposed in this paper differentiates the role of continental glacier, ice sheets and sea ice in the process of global or eustatic sea level rise. It shows that melting of sea ice is not responsible for global or eustatic sea level change. However convoluted effect of melting of continental glaciers and ice sheets and thermal expansion of ocean water due to increasing ocean heat budget is responsible for recent eustatic sea level rise.

Impact of Climatic Factors on Albacore Tuna <i>Thunnus alalunga</i> in the South Pacific Ocean

Over the years there has been growing interest regarding the effects of climatic variations on marine biodiversity. The exclusive economic zones of South Pacific Islands and territories are home to major international exploitable stocks of albacore tuna (Thunnus alalunga); however the impact of climatic variations on these stocks is not fully understood. This study was aimed at determining the climatic variables which have impact on the time series stock fluctuation pattern of albacore tuna stock in the Eastern and Western South Pacific Ocean which was divided into three zones. The relationship of the climatic variables for the global mean land and ocean temperature index (LOTI), the Pacific warm pool index (PWI) and the Pacific decadal oscillation (PDO) was investigated against the albacore tuna catch per unit effort (CPUE) time series in Zone 1, Zone 2 and Zone 3 of the South Pacific Ocean from 1957 to 2008. From the results it was observed that LOTI, PWI and PDO at different lag periods exhibited significant correlation with albacore tuna CPUE for all three areas. LOTI, PWI and PDO were used as independent variables to develop suitable stock reproduction models for the trajectory of albacore tuna CPUE in Zone 1, Zone 2 and Zone 3. Model selection was based on Akaike Information Criterion (AIC), R2 values and significant parameter estimates at p < 0.05. The final models for albacore tuna CPUE in all three zones incorporated all three independent variables of LOTI, PWI and PDO. From the findings it can be said that the climatic conditions of LOTI, PWI and PDO play significant roles in structuring the stock dynamics of the albacore tuna in the Eastern and Western South Pacific Ocean. It is imperative to take these factors into account when making management decisions for albacore tuna in these areas.

Influence of Climatic Conditions on the Time Series Fluctuation of Yellowfin Tuna &amp;lt;i&amp;gt;Thunnus albacares&amp;lt;/i&amp;gt; in the South Pacific Ocean

Yellowfin tuna (Thunnus albacares) is one of the most commercially important fish species for South Pacific island nations and territories and for effective conservation efforts it is important to understand the factors which affect its time series pattern. Our research was aimed at elucidating the climatic factors which affected the trajectory of the yellowfin tuna stock in the Eastern and Western South Pacific Ocean. We utilized various climatic factors for the years t - n with n = 0, 1, ..., 8 and investigated their statistical relationship with the catch per unit effort (CPUE) of yellowfin tuna stock from 1957-2008 for three South Pacific zones ranging from the East to the West Pacific Ocean within the coverage area of the Western and Central Pacific Convention Area. Results showed that the climatic conditions of: (i) the global mean land and ocean temperature index (LOTI), (ii) the Pacific warm pool index (PWI) and (iii) Southern Oscillation Index (SOI) had significant relationship with the CPUE of yellowfin tuna in all three zones. LOTI, PWI and SOI were used as independent variables and fitted through modeling to replicate the CPUE trajectory of the yellowfin tuna in Zone 1, Zone 2 and Zone 3. Model selection was based on significant parameter estimates (p < 0.05), Akaikes Information Criterion (AIC) and R2 values. Models selected for all three zones had LOTI, PWI and SOI as the independent variables. This study shows that LOTI, PWI and SOI are climatic conditions which have significant impact on the fluctuation pattern of the yellowfin tuna CPUE in the Eastern and Western South Pacific Ocean. From the findings of this study it can be recommended that when management decisions are made for yellowfin tuna fishery conservation and sustainability in the Eastern and Western South Pacific, it is imperative to take the effect of climatic factors into account.

Factors Affecting Japanese Pond Smelt (&amp;lt;i&amp;gt;Hypomesus nipponensis&amp;lt;/i&amp;gt;) Stock Trajectory in Lake Kasumigaura and Kitaura

The Japanese pond smelt (Hypomesus nipponensis) stock has been observed to fluctuate quite rigorously over the years with sustained periods of low catch in Lake Kasumigaura and Kitaura of the Ibaraki prefecture, Japan which would adversely affect the socioeconomic livelihood of the local fishermen and fisheries industry. This study was aimed at determining the factors affecting the stock fluctuation of the pond smelt through the different years in the two lakes. Through exploratory analysis it was found that the pond smelt had significant relationship with total phosphorus (TP) level in both lakes. The global mean land and ocean temperature index (LOTI) was also found to be indirectly related to the pond smelt stock in lake Kasumigaura and Kitaura at the latitude band of 24°N to 90°N (l). Both TP and LOTI had inverse relationship with pond smelt trajectory in both lakes. For both Lake Kasumigaura and Kitaura, TP for the individual lakes and LOTI (l) were used as independent variables using generalized linear model and response surface methods for modeling the stock dynamics of the pond smelt in the two lakes. Model selection was based on significant parameter estimates (p < 0.05), Akaikes Information Criterion and R2 values. Phosphorus loading is an indication of increasing anthropogenic activities in the surrounding area having negative impact on the pond smelt population. When management decisions are being made regarding pond smelt fishery and sustainability plans in the Ibaraki prefecture, the effects of TP and LOTI should be taken into account. Future research needs to be directed towards deeper understanding the mechanisms by which TP and LOTI affect pond smelt population in Lake Kasumigaura and Kitaura for more effective management.

Simulation of global ocean acidification and chemical habitats of shallow- and cold-water coral reefs

Using the UVic Earth System Model, this study simulated the change of seawater chemistry and analyzed the chemical habitat surrounding shallow- and cold-water coral reefs from the year 1800 to 2300 employing RCP2.6, RCP4.5, RCP6.0, and RCP8.5 scenarios. The model results showed that the global ocean will continue to absorb atmospheric CO2. Global mean surface ocean temperature will rise 1.1–2.8 K at the end of the 21st century across RCP scenarios. Meanwhile, the global mean surface ocean pH will drop 0.14–0.42 and the ocean surface mean concentration of carbonate will decrease 20%–51% across the RCP scenarios. The saturated state of sea water with respect to calcite carbonate minerals (Ω) will decrease rapidly. During the pre-industrial period, 99% of the shallow-water coral reefs were surrounded by seawater with Ω > 3.5 and 87% of the deep-sea coral reefs were surrounded by seawater with aragonite supersaturation. Within the 21st century, except for the high mitigation scenario of RCP2.6, almost none shallow-water coral reefs will be surrounded by seawater with Ω > 3.5. Under the intensive emission scenario of RCP8.5, by the year 2100, the aragonite saturation horizon will rise to 308 m under the sea surface from 1138 m at the pre-industrial period, thus 73% of the cold-water coral reefs will be surrounded by seawater with aragonite undersaturation. By the year 2300, only 5% of the cold-water coral reefs will be surrounded by seawater with aragonite supersaturation.

Climate-forced change in Hudson Bay seawater composition and temperature, Arctic Canada

Global climate change impacts marine ecosystems, directly and indirectly, especially in the Arctic and Antarctic. We show the first long-term (1920–2011) time-series of oceanographic change in Hudson Bay, an arctic marine ecosystem, based on coupled brachiopod-calcite stable and clumped isotope results. Long-term decrease in brachiopod δ13C parallels that of seawater-DIC in Hudson Bay, and after considering its seasonal sea ice coverage, it is similar to that of the 13C-Suess effect observed in the North Atlantic and other regions. Acidification of Hudson Bay seawater leads warming by about 10–20years, and with intensified warming from the 1970s to 2010s closely coupled to earlier sea-ice breakup. Post-industrial warming of Hudson Bay is initially slow, but in later years, faster and of greater magnitude than of the coeval global oceans. Our observations for the past 90years suggest that climate-forced change contributed to an average increase of about 0.1°C and 3.6°C in sea-surface water temperature of Hudson Bay over the first 50 and subsequent 40years, respectively. This 3.7°C post-industrial warming of Hudson Bay seawater is about six times the 0.67°C increase observed during the past 100years in global ocean sea-surface temperature, which is about double the postulated increase of about 2°C for polar regions. Our results are consistent with the general notion that polar marine environments, such as Hudson Bay, can serve as sensitive indicators of change in climate, and of change still to come for lower latitude ecosystems.

Climate change and water availability in Indian agriculture: Impacts and adaptation

Climate is a very decisive factor in water resource availability of a region. Warming of the climate system in recent decades is evident from increase in global average air and ocean temperatures, widespread melting of snow and ice, and rising global sea level. The hydrological cycle is intimately linked with changes in atmospheric temperature and radiation balance. A warmer climate may lead to intensification of the hydrological cycle, resulting in higher rates of evaporation and increase of liquid precipitation. These processes, in association with a shifting pattern of precipitation, may affect the spatial and temporal distribution of runoff, soil moisture, groundwater reserves etc. and may increase the frequency of droughts and floods. Agricultural demand, particularly for irrigation water is considered more sensitive to climate change. A change in field-level climate may alter the need and timing of irrigation. Increased dryness may lead to increased demand, but demand may be reduced if soil moisture content rises at critical times of the year. It is projected that most irrigated areas in India would require more water around 2025 and global net irrigation requirements would increase relative to the situation without climate change by 3.5–5% by 2025, and 6–8% by 2075. The effect of climate change on water resources may be mitigated through better water harvesting through the creation of micro-storage facilities in watersheds. These would not only provide supplemental irrigation but also recharge the groundwater aquifers.