Warm Surface Water Research Articles

Impact of warming shelf waters on ice mélange and terminus retreat at a large SE Greenland glacier

Abstract. By the end of 2018 Kangerlussuaq Glacier in southeast Greenland had retreated further inland than at any time in the past 80 years and its terminus was approaching a region of retrograde bed slope from where further rapid retreat would have been inevitable. Here we show that the retreat occurred because the glacier failed to advance during the winters of 2016/17 and 2017/18 owing to a weakened proglacial mélange. This mixture of sea ice and icebergs is normally rigid enough to inhibit calving in winter, but for 2 consecutive years it repeatedly collapsed, allowing Kangerlussuaq Glacier to continue to calve all year round. The mélange break-ups followed the establishment of anomalously warm surface water on the continental shelf during 2016, which likely penetrated the fjord. As calving continued uninterrupted from summer 2016 to the end of 2018 the glacier accelerated by 35 % and thinned by 35 m. These observations demonstrate the importance of near-surface ocean temperatures in tidewater glacier stability and show that it is not only deep-ocean warming that can lead to glacier retreat. During winter 2019 a persistent mélange reformed and the glacier readvanced by 3.5 km.

Seasonal and diurnal trends of surface refractivity in a tropical environment using ground-based automatic weather stations

The seasonal and diurnal trends of surface refractivity were derived using International Telecommunication Union Radio assembly model (ITU-R P.453-13) in two locations of entirely different vegetation characteristics in Nigeria. Atmospheric refractivity is a function of temperature, pressure as well as humidity. These meteorological variables were applied to the model to compute the refractivity parameter. Atmospheric refraction or refractivity is a key component in radio wave propagation. Real-time measurement data from a network of ground-based automatic weather station (AWS) installed at 3 m height were used and the monthly trends of surface refractivity at both stations (Lagos and Anyigba) were derived; the trends showed a month-to-month variability signifying the dynamic nature of the Earth’s atmosphere. The monthly trends in both stations show high refractivity values in the rainy months and low refractivity values in the dry months. A drop in refractivity value was observed in Lagos in the month of August, due to the cessation in rainfall as a result of a phenomenon referred to as August break. The diurnal variations were also determined and results obtained showed that the lowest refractivity value in the dry season observed in Lagos is higher than the highest refractivity value in rainy season observed in Anyigba. This is attributed to the fact that Lagos is located along the coast of the South Atlantic Ocean, therefore, the monsoon has a direct influence on its atmosphere, while Anyigba is an inland station with a mixture of savannah vegetation. Overall, the diurnal variations show high values in the morning and evening hours and low values in the afternoon hours in both seasons in Anyigba, while in Lagos we observed a surprising result, such as a rise in refractivity value at pre-noon and a post-noon drop. This unacquainted observation is probably due to excessive precipitation in the area caused by the influence of massive emissions from the South Atlantic Ocean, these emissions are mainly a result of the trapped heat due to warming of surface water.

Effect of Culture Depth and Season on the Condition and Reproductive Indices of Blue Mussels (Mytilus edulis L.) Cultured in a Cold-Water Coastal Environment

Condition, growth, and reproductive indices of blue mussels (Mytilus edulis) grown in deep and shallow sites were studied from May to December 2016 in the South Arm region of Notre Dame Bay, Newfoundland. The region was shown to be characterized by a seasonal thermocline that formed in April and lasted to October annually, resulting in a cold-water deep layer (mean annual temperature: 4.36 ± 5.1°C) and a comparatively warmer surface layer (mean annual temperature: 5.81 ± 6.3°C). The deepwater culture sites extended into the cold-water layer and the shallow sites were typically in the warmer layer above. Mussels grown in shallow sites had longer and heavier shells than those from deepwater sites, likely linked to warmer surface waters. Both reproductive and physiological condition indices were high for mussels from both culture depths in May. Physiological condition declined for both deep and shallow cultured mussels from May through to August. Mussels from deep sites, however, had a higher overall mean dry tissue weight: wet tissue weight ratio for the study period. Reproductive indices, including measurements of reproductive output, declined for shallow mussels from May through to August, but remained high for deep mussels until August when a significant spawn occurred for mussels from both depths. In addition, mussels from deep sites were observed to maintain themselves in a prespawning ripe stage for a longer period than those from shallow sites. Variations in physiological and reproductive indices for mussels from each respective culture depth were thought to be linked to differences in the environmental characteristics of the deep and shallow water layers, including rate of temperature change and potential differences in phytoplankton quality and energetics. The additional data provided in the present study add to the current understanding of the effects of the deepwater environment on mussel reproduction patterns and its relationship to production meat yield. The data will help in highlighting the benefits of using deepwater sites leading to increased environmental sustainability for mussel culture in subarctic coastal environments such as those on the north coast of Newfoundland.

Habitable Snowballs: Temperate Land Conditions, Liquid Water, and Implications for CO2 Weathering

AbstractHabitable planets are commonly imagined to be temperate planets like Earth, with areas of open ocean and warm land. In contrast, planets in snowball states, where oceans are entirely ice covered, are believed to be inhospitable. However, we show using a general circulation model that terrestrial planets in the inner habitable zone are able to support large unfrozen areas of land while in a snowball state. Due to their lower albedo, these unfrozen regions reach summer temperatures in excess of 10 °C. Such conditions permit CO2 weathering, suggesting that continental weathering can provide a mechanism for trapping planets in stable snowball states. The presence of land areas with warm temperatures and liquid surface water motivates a more‐nuanced understanding of habitability during these snowball events.

Amazonian trees show increased edge effects due to Atlantic Ocean warming and northward displacement of the Intertropical Convergence Zone since 1980.

Recent investigations indicate a warming of Atlantic Ocean surface waters since 1980, probably influenced by anthropic actions, inducing rainfall intensification mainly during the rainy season and slight reductions during the dry season in the Amazon. Under these climate changes, trees in upland forests (terra firme) could benefit from the intensification of the hydrological cycle and could also be affected by the reduction of precipitation during the dry season. Results of dendrochronological analyses, spatial correlations and structural equation models, showed that Scleronema micranthum (Ducke) Ducke (Malvaceae) trees exposed in fragmented areas and to edge effects in Central Amazonian terra firme forest were more sensitive to the increase in the Atlantic Ocean surface temperature and consequent northward displacement of the Intertropical Convergence Zone, mainly during the dry season. Therefore, we proved that in altered and potentially more stressful environments such as edges of fragmented forests, recent anthropogenic climatic changes are exerting pressure on tree growth dynamics, inducing alterations in their performance and, consequently, in essential processes related to ecosystem services. Changes that could affect human well-being, highlighting the need for strategies that reduce edge areas expansion in Amazon forests and anthropic climate changes of the Anthropocene.

Effects of climate changes on the microbial activities and prokaryotic abundances in the euphotic layer of the Central Mediterranean Sea

Prokaryotic microorganisms are at the base of marine food web and are sensitive to climate changes. In the Mediterranean Sea, an important link between surface water warming and microbial activities is hypothesized to exist on a seasonal and inter-annual scale, with high amounts of organic matter utilized by prokaryotes and recycled in warm periods. To test this hypothesis, from 1998 to 2013, the prokaryotic abundance and microbial activities (enzymatic activities, prokaryotic heterotrophic production, and respiration), together with trophic parameters (chlorophyll, particulate organic carbon, and nitrogen), were measured in the euphotic layer of the Ionian Sea (Central Mediterranean). A statistical simultaneous analysis of the environmental and prokaryotic data was performed with the aim of depicting the evolution of microbial activities and their implications in the biogeochemical cycles. Results showed that despite the large spatial and temporal variability, temperature was the main factor affecting the variability of microbial abundance and metabolism with significant differences on both seasonal and inter-annual scales. Particularly interesting is the increase of production in summer and of the respiration in winter. In spite of low levels of chlorophyll and organic carbon, an increase of prokaryotic heterotrophic production, coupled with that of alkaline phosphatase, was found. As a consequence, the increase of prokaryotic biomass was bottom-up sustained. Most of prokaryotic activities and respiration rates were significantly correlated to organic carbon pools; the process of organic matter decomposition was frequently enhanced at higher temperature, and both prokaryotic production and growth efficiency increased in summer. In view of climate changes, the rise in temperature was associated to the increase of heterotrophic activities and this trend can have a predictive value to describe the microbial processes in the Central Mediterranean Sea.

A place in space - the horizontal vs vertical factors that influence zooplankton (Rotifera, Crustacea) communities in a mesotrophic lake

The factors that influence plankton distribution in lakes are currently widely debated. The primary objective of this study was to determine a combination of factors that influence the three-dimensional distribution patterns of both rotifer and crustacean communities in a pelagic ecosystem. We compared the abiotic (temperature, oxygen and nutrients) and biotic (phytoplankton) factors that affect the horizontal and vertical distribution of zooplankton in different habitat conditions in Lake Wigry. The results of our study indicate that the vertical gradient in a water profile is much more important for microcrustaceans than horizontal changes in environmental conditions, whereas Rotifera showed a strong spatial autocorrelation when connected with differences in trophic status. Generally, large zooplankton prefer cold, darker waters of the metalimnion-hypolimnion, while smaller zooplankton prefer the warm epilimnion. This niche segregation in water profiles promotes a large diversity of pelagic zooplankton. The vertical distribution of dominant Daphnia cucullata was strongly related to the phytoplankton distribution. Moreover, we found that the large-bodied Daphnia cucullata prefers the lower water layers, despite the presence of less optimal food resources, while smaller individuals clearly prefer the warm surface water with high quality resources.

Shallow plant-dominated lakes - extreme environmental variability, carbon cycling and ecological species challenges.

Submerged plants composed of charophytes (green algae) and angiosperms develop dense vegetation in small, shallow lakes and in littoral zones of large lakes. Many small, oligotrophic plant species have declined due to drainage and fertilization of lakes, while some tall, eutrophic species have increased. Although plant distribution has been thoroughly studied, the physiochemical dynamics and biological challenges in plant-dominated lakes have been grossly understudied, even though they may offer the key to species persistence. Small plant-dominated lakes function as natural field laboratories with eco-physiological processes in dense vegetation dictating extreme environmental variability, intensive photosynthesis and carbon cycling. Those processes can be quantified on a whole lake basis at high temporal resolution by continuously operating sensors for light, temperature, oxygen, etc. We explore this hitherto hidden world. Dense plant canopies attenuate light and wind-driven turbulence and generate separation between warm surface water and colder bottom waters. Daytime vertical stratification becomes particularly strong in dense charophyte vegetation, but stratification is a common feature in small, shallow lakes also without plants. Surface cooling at night induces mixing of the water column. Daytime stratification in plant stands may induce hypoxia or anoxia in dark bottom waters by respiration, while surface waters develop oxygen supersaturation by photosynthesis. Intensive photosynthesis and calcification in shallow charophyte lakes depletes dissolved inorganic carbon (DIC) in surface waters, whereas DIC is replenished by respiration and carbonate dissolution in bottom waters and returned to surface waters before sunrise. Extreme diel changes in temperature, DIC and oxygen in dense vegetation can induce extensive rhythmicity of photosynthesis and respiration and become a severe challenge to the survival of organisms. Large phosphorus pools are bound in plant tissue and carbonate precipitates. Future studies should test the importance of this phosphorus sink for ecosystem processes and competition between phytoplankton and plants.

Paleoenvironment reconstruction of the Proterozoic carbonate platform, Ombella-M'poko formation (Central African Republic)

Petrographic studies, geochemistry, δ13C and δ18O isotopes have been used to characterize the well-preserved carbonate depositional environments of the Bobassa and Ndimba unit in the 640-565 Ma Ombella-M'poko Formation, Central African Republic. The carbonate facies are mainly composed of calcite, dolomite and quartz with some accessory minerals (opaque minerals, muscovite and pyrite). The Ca/Mg ratios show that the Bobassa carbonates are slightly metamorphosed dolomitic limestones, while those of Ndimba correspond to slightly metamorphosed highly dolomitic limestones and cipolins. The Bobassa unit recorded a depositional evolution from fluvial to peritidal environments in a possible tectonically active platform as evidenced by changes of lithology and slump structures. The Ndimba was deposited in a tidal-influenced fluvio-lacustrine environment under dry conditions. Geochemistry revealed that the Bobassa and Ndimba units recorded variable redox conditions from anoxic to oxic. The PAAS-normalized REE + Y distributions indicate that the both units were slightly altered by freshwaters and detrital materials in reduced and acidic environments. The lowest δ18O and highest δ13C values suggest warm surface waters and deeper water column respectively. The carbon isotope profiles of Bobassa and Ndimba units show values varying between −0.89 and −0.34‰ that are not stratigraphic coeval with the cap carbonates δ13C profiles deposited in the aftermath Marinoan Glaciation, but rather are correlated to the middle to upper part of the Schisto-Calcaire Group in Gabon and Republic of Congo and the time-equivalent Lukala Subgroup in DRC.

Deep ocean 14C ventilation age reconstructions from the Arctic Mediterranean reassessed

The present-day ocean ventilation in the Arctic Mediterranean (Nordic Seas and Arctic Ocean), via transformation of northward inflowing warm Atlantic surface water into cold deep water, affects regional climate, atmospheric circulation and carbon storage in the deep ocean. Here we study the glacial evolution of the Arctic Mediterranean circulation and its influence on glacial climate using radiocarbon reservoir-age reconstructions on deep-sea cores from the Fram Strait that cover the late glacial period (33,000–20,000 yr ago; 33–20 ka). Our results show high Benthic-Planktic 14C age differences of ∼1500 14C years 33–26.5 ka suggesting significant water column stratification between ∼100–2600 m water depth, and reduction and/or shoaling of deep-water formation. This phase was followed by break-up of the stratification during the Last Glacial Maximum (LGM; 26–20 ka), with Benthic-Planktic 14C age differences of ∼250 14C years, likely due to enhanced upwelling. These ocean circulation changes potentially contributed to the final intensification phase of glaciation via positive cryosphere-atmosphere-ocean circulation-carbon cycle feedbacks. Our data also do not support ‘extreme aging’ of >6000 14C years in the deep Arctic Mediterranean, and appear to rule out the proposed outflow of very old Arctic Ocean water to the Nordic Seas during the LGM and to the subpolar North Atlantic Ocean during the deglacial period.

Palaeoceanographic reconstruction of surface-ocean changes in the southern Norwegian Sea for the last ~130,000 years based on diatoms and with comparison to foraminiferal records

Fossil marine diatom assemblages in a sediment core from the central northern Faroe slope in the Norwegian Sea were used to reconstruct palaeoceanographic changes in the surface water mixed layer from the last ~130,000 years (Marine Isotope Stage (MIS) 6/5 transition to MIS 1 (including the Eemian and Holocene interglacials) and to compare the results with previously published results on planktic foraminifera representing the subsurface conditions of the thermocline. Diatom floras from MIS 5 of the Nordic seas have rarely been studied in detail before and never the entire period from pre-Eemian to present. The composition of diatom species together with maxima in absolute abundance of diatoms, indicate two periods of warmer sea surface temperatures correlating with the Eemian and Holocene interglacials, respectively. The Eemian differs from the Holocene in that the Iceland-Faroe Front never developed, suggesting the cold East Icelandic Current (originating from the East Greenland Current) running north of Iceland was reduced or more mixed with Atlantic water than during the Holocene and that the surface temperature and salinity gradients were weaker. The northern Faroe slope was in the early Weichselian of MIS 5d–5a mainly influenced by weaker inflow of Atlantic water and stronger influence of the East Icelandic Current and by seasonal sea-ice cover. During the later part of the Weichselian (MIS 4–MIS 2) cold conditions prevailed with extensive sea-ice cover except during the warmer interstadials. The diatom floras were more sensitive to climate changes than the planktic foraminifera and indicate longer periods with warm surface conditions, and increased influence of the warm Atlantic surface water from the Faroe Current in MIS 5, suggesting a shallower and much steeper thermocline during the transitional periods compared to today. The diatoms are good indicators for Atlantic water inflow and possible convection in the Nordic seas, not merely reflecting orbital variations in insolation as previously suggested.

Vertical distributions of blooming cyanobacteria populations in a freshwater lake from LIDAR observations

The vertical distributions of freshwater cyanobacteria populations are important to plankton community structure, ecology and for influencing water column optical properties relevant to remote sensing. In August of 2014, we examined the vertical structure of a cyanobacteria bloom across the western basin of Lake Erie with new technologies, including LIDAR and a digital holographic system. In addition, vertical profiles of environmental and optical properties were made. The active LIDAR penetrated the water column, and provided a detailed picture of the particle distribution for the whole water column. The holographic system provided digital images processed for particle size, count and identification of Microcystis and Planktothrix - the two main cyanobacteria genera that were present. The correlations between the LIDAR backscatter intensity and the cyanobacteria cell counts from holography averaged to 0.53 and ranged from −0.13 to 0.96 based on nearest matchups. The vertical structure of the overall cyanobacteria population was influenced by wind speed, and to a lesser degree the solar heating of surface waters. On a more detailed level, Microcystis populations were consistently nearer to the surface relative to Planktothrix. Pigments from surface samples revealed a higher degree of photoprotection for Planktothrix-dominated communities. The vertical distributions of the cyanobacteria genera were related to light intensity in the water column and known tolerances and/or preferences for each genus. Vertical profiles of optical properties supported the patterns seen in the LIDAR and holographic data, and had direct implications on the exiting light field. These combined data provide a unique view into the natural variations in spatial (vertical and horizontal) distribution patterns of cyanobacteria and resulting impacts on remote sensing detection and associated interpretations, and demonstrate the potential for these technologies to observe cyanobacteria in lake environments.

Differentiating the Effects of Climate Change-Induced Temperature and Streamflow Changes on the Vulnerability of Once-Through Thermoelectric Power Plants.

Thermoelectric power plants with once-through cooling systems generated 30% (∼300 GW) of U.S. electricity in 2016. Factors that reduce once-through cooling capacity and thus power output are environmental regulations, warming surface waters, and drought. The latter two may become more frequent as global climate changes. Previous research indicates that reduction in power plant capacity caused by environmental regulations can be significant while that by surface water warming is minor. Here, we address the effect of droughts on power output, which until now has remained conflated with temperature impacts. We do this using a widely used electricity generation model alongside hourly operational and meteorological data for 52 once-through plants located across the U.S. The effect of drought on plant output is examined for different water-availability and temperature scenarios, with and without regulations on plant water discharge. We find that if surface waters warm 3 °C and river discharges drop 20%, droughts would account for ≤20% of total capacity reduction depending on the plant, warming surface waters ≤2.3%, and environmental regulations up to 80%. This suggests that maintaining environmental regulations will require the continued conversion of plant cooling systems from once-through to recirculating, and mitigating climate impacts will require more stringent drought-specific watershed management.

A new perspective of the 2014/15 failed El Ni\xf1o as seen from ocean salinity

This study investigates the 2014/15 failed El Niño using salinity from an ocean general circulation model. The results indicate that subsurface processes were especially strong in the summer of 2014 and they led to positive sea surface salinity anomalies in the central equatorial Pacific. The positive sea surface salinity anomalies induced a westward displacement of the sea surface salinity front that represents the eastern boundary of the western Pacific warm pool, preventing the warm surface water from shifting eastward as seen in a typical El Niño event. In the meantime, more salty water was transported equatorward by a strengthening subtropical cell in the South Pacific. The enhanced subsurface processes in the central equatorial Pacific conveyed the salinity anomalies of subtropical origin to the sea surface and were largely responsible for the sea surface salinity variability but had less impacts on sea surface temperature during the 2014/15 failed El Niño, suggesting some potential advantage of ocean salinity in the El Niño-Southern Oscillation prediction.

The Curious Association between Hadley Circulation Intensity and the Meridional Distribution of Tropical Cyclones in the Eastern North Pacific

It has recently been shown that an interesting inverse relationship exists between the strength of the overturning in the regional boreal Hadley circulation and tropical cyclone genesis and lifetime maximum intensity latitudes in the eastern North Pacific. One of the particularly curious aspects of this association is its uniqueness to this ocean basin. We show here that this result can be understood as the outcome of an equatorward shift in the local Intertropical Convergence Zone (ITCZ) and a moderate reduction of tropical vertical shear. These two factors are not necessarily concomitant. The magnitude of the vertical shear change is low enough to suggest that the primary physical mechanism behind this inverse relationship is the equatorward shift in the ITCZ. Since a significant proportion of tropical cyclone genesis results from aggregated convective cells forming into a coherent convective vortex and being shed from the ITCZ, this shift is apparently sufficient to explain the observed association. The equatorward shift in the ITCZ is potentially the result of a relative warming of the Southern Hemisphere in the boreal tropical cyclone season. This more equatorward ITCZ, located over warmer surface waters, presumably explains the more intense Hadley circulation, despite a reduction of the large-scale boreal meridional temperature gradient. Although, these links require further research.

A Wedge Mechanism for Summer Surface Water Inflow Into the Ross Ice Shelf Cavity

AbstractOcean heat supply to ice shelves has a significant impact on the long‐term evolution of ice shelves. Intrusions of warm surface waters into the frontal region of the cavity, known as “Mode 3” circulation, are capable of melting the ice shelf base. However, ablation of the vertical walls of the ice shelf front has, to date, received little attention. Here we propose a mechanism for Mode 3 circulation that is aided by ice shelf front ablation: Direct contact of warm Antarctic Surface Water with the ice wall generates meltwater that buoyantly ascends the vertical face and leads to formation of a “wedge” of fresher water immediately adjacent to the wall. This wedge, which thins with distance from the ice shelf front, allows isopycnals to curve gently downward, creating an efficient conduit by which surface waters moved by other forces such as tidal flow and eddies enter an ice shelf cavity with minimal mixing. Here we use new and existing observational data from the Ross Sea and the Ross Ice Shelf cavity to demonstrate the existence of the wedge. Our analysis and a review of the literature suggest that the freshwater wedge structure is a pervasive feature of the Western Ross Sea in summer and enhances other inflow mechanisms.

What is the El Niño–Southern Oscillation?

The El Niño–Southern Oscillation (ENSO) is a large-scale climatic phenomenon that originates in the tropical Pacific but affects global climate patterns. The warm phase is known as El Niño, and the cold phase, La Niña. El Niño occurs irregularly every 2 to 7 years and generally peaks during Northern Hemisphere winter. In a normal year, when ENSO is inactive, the equatorial Pacific trade winds blow from east to west. The winds push the warmer surface water towards the west, and colder water rises up from deeper in the ocean to replace it. This creates an east–west difference in sea-surface temperature (SST) and hence an east–west difference in sea level air pressure that maintains the trade winds and so drives a positive feedback loop (Figure 1(a)). During an El Niño year, the east–west SST difference weakens, the air pressure difference weakens, and the trade winds and their effects on the ocean weaken, so the eastern Pacific warms (Figure 1(b)). During a La Niña year, the opposite ­happens: the east–west difference in temperature strengthens, the pressure difference strengthens, and the trade winds and their effects on the ocean strengthen, so the east Pacific cools further (Figure 1(c)). Such changes in sea-surface temperature affect the atmosphere over vast areas, with both local and global repercussions. Locally, during the El Niño phase, the associated atmospheric circulation changes drive increased atmospheric convection and precipitation over the central and eastern Pacific, while rainfall is reduced over the western Pacific. These changes have remote impacts throughout the tropics but also at higher latitudes via large-scale motion of the atmosphere, especially when ENSO is at its strongest in winter. A network of ocean buoys measure sea surface temperature, ocean currents and the wind. Satellites also provide surface temperature and ocean current data, providing the ability to monitor ENSO in real time. El Niño months can be predicted in advance by measuring the heat content of the upper ocean, one of the precursors for the onset of El Niño, and then using climate models to predict its evolution. Although various criteria exist, an El Niño event is normally said to be underway when the sea surface temperature in the equatorial Pacific (officially called the ‘Niño 3.4’ region) rises by +0.5 degC above the historical average for at least three months in a row. The strongest impacts are experienced by those countries near the tropical Pacific origin of ENSO. Changes in surface temperature, wind and moisture affect rainfall intensity and patterns, which can lead to extreme events such as flooding and drought. During an El Niño event, Peru, Ecuador and southeastern parts of South America receive heavy rainfall. In northern Brazil, drier conditions or even drought may result. Indonesia, South Asia and parts of Australia are also more likely to experience drought during the El Niño phase. The change in weather patterns associated with El Niño can greatly impact the economy, in particular agriculture, water resources, fisheries and public health. ENSO also has a strong influence on the occurrence and intensity of tropical cyclones, and Atlantic hurricane activity weakens during El Niño but strengthens during La Niña. In the UK we experience the socio-economic impacts of an El Niño event, partly through increased food prices, and there are effects on the jet stream and European weather, especially in late winter, when El Niño increases the chances of cold snaps and La Niña increases the chances of wet and stormy conditions. El Niño releases heat to the atmosphere and increases subsequent global temperatures. For example, global average temperatures for 2016 were around 1.1 degC above pre-industrial values, and the strong El Niño episode of 2015/2016 partly contributed to this rise. However, researchers have concluded that the warming from this El Niño accounted for only about 0.2 degC of this overall figure. Because of the large event-to-event variability of El Niño, we don't have enough past years of observations to show how climate change may impact it. There is now some evidence that rainfall may increase during El Niño events in the future and that we may even see more very strong ENSO events, but these remain active research questions. Real-time observational monitoring of the tropical ocean and El Niño are available from NOAA at: https://www.pmel.noaa.gov/tao/drupal/disdel/ Met Office Hadley Centre forecasts of El Niño and global temperature can be found here: https://www.metoffice.gov.uk/research/climate/seasonal-to-decadal/gpc-outlooks/el-nino-la-nina Forecasts from other prediction models provided by the International Research Institute for Climate and Society are available here: https://iri.columbia.edu/our-expertise/climate/forecasts/enso/current/

Foraging habitat choice of White-tailed Tropicbirds revealed by fine-scale GPS tracking and remote sensing.

BackgroundThe introduction of animal tracking technology has rapidly advanced our understanding of seabird foraging ecology. Tracking data is particularly powerful when combined with oceanographic information derived from satellite remote sensing, allowing insights into the functional mechanisms of marine ecosystems. While this framework has been used extensively over the last two decades, there are still vast ocean regions and many seabird species for which information is scarce, particularly in tropical oceans.MethodsIn this study we tracked the movement at high GPS recording frequency of 15 White-tailed Tropicbirds (Phaethon lepturus) during chick-rearing from a colony in Fernando de Noronha (offshore of Northeast Brazil). Flight behaviours of travelling and searching for food were derived from GPS data and examined in relation to satellite-sensed oceanographic variables (sea surface temperature, turbidity and chlorophyll-a concentration).ResultsWhite-tailed Tropicbirds showed marked preference for clear and warm sea surface waters, which are indicative of low primary productivity but are likely the best habitat for preying upon flying fish.DiscussionThese findings are consistent with previous studies showing that foraging habitat choices of tropical seabirds may not be driven by primary productivity, as has been widely shown for non-tropical species.

Changes in mixing depth reduce phytoplankton biomass in an Arctic lake: Results from a whole-lake experiment

ABSTRACTResearch has revealed contradictory responses of primary producers in Arctic lakes to increasing temperatures, making it unclear how future warming and climate change will alter lake productivity. We conducted a whole-lake manipulation to examine the effect of altered thermal structure on phytoplankton biomass in a lake in Greenland, one of the most rapidly warming regions of the world. Deepened lake mixing (from 4 to 8 m) in the experimental lake led to significant declines in phytoplankton biomass in the sediment traps despite warmer surface waters, indicating that changes in mixing depth may negate a positive, direct effect of warming on primary producer biomass. Light limitation (induced by deeper mixing) of phytoplankton played a greater role than temperature in structuring these Arctic lake phytoplankton communities. To put the manipulation in context, we surveyed twenty-four lakes across western Greenland to determine the strongest regional predictors of phytoplankton density. Across the landscape, lake chemistry and light attenuation in the epilimnion were the most important predictors of algal assemblages in the survey lakes. Though temperature can directly influence lake ecosystems, multiple factors will affect mixing depths of Arctic lakes, potentially leading to variable effects of warming on phytoplankton biomass and community structure.

Techno-economic analysis of multipurpose OTEC power plants

Ocean Thermal Energy Conversion (OTEC) is a promising technology to provide sustainable and dispatchable energy supply to oceanic coastal areas and islands. It exploits the temperature difference between deep cold ocean water and warm tropical surface water in an Organic RankineCycle (ORC), guaranteeing a continuous and dispatchable electric production, overcoming one ofthe most critical issue of renewable generators such as PV or wind turbines. Despite the technological maturity of ORC application to OTEC systems, it still presents technical and economicbarriers mainly related to their economic feasibility, large initial investments as well as heavy and time demanding civil installation works. To overcome such issues, multipurpose OTEC plants are proposed, producing electrical power as well as other products, such as useful thermal power (e.g. ambient cooling) and desalinated water. Since OTEC engineering is still at a lowdegree of maturity, there are no widespread and established tools to facilitate OTEC feasibility studies and to allow performance and cost optimization. Therefore, in this paper, a new tool for techno-economic analysis and optimization of multipurpose OTEC plants is presented. Starting from a detailed database of local water temperature and depth, the approach allows to provide a quantitative insight on the achievable performance, required investment, and expected economic returns, allowing for a preliminary but robust assessment of site potential as well as plant size. After the description of the techno-economic approach and related performance and cost functions, the tool is applied to an OTEC power plant case study in the range of 1 MW gross electrical power, including a preliminary assessment of scaling-up effects.