Open Ocean Areas Research Articles

Atmospheric Optical Turbulence Characteristics over the Ocean Relevant to Astronomy and Atmospheric Physics

Due to the space and time constraints of turbulence measurement equipment and the experiment scene, it is difficult to obtain the atmosphere refractive index structure constant over the ocean. In this paper, the characteristics of atmospheric optical turbulence in offshore and open ocean conditions are summarized by analyzing the meteorological data obtained from two ocean atmospheric optical parameter field experiments. Because of the influence of land undersurface, the turbulence strength in offshore conditions is roughly the same as that on land and presents different characteristics in open ocean. Compared with the offshore area, the turbulence strength over the open ocean near-surface decreases during the day and increases at night, and the diurnal variation characteristics weaken. The turbulence strength profiles over the offshore area show different characteristics at different times, where the turbulence strength in the morning is higher than that in the evening. By retrieving the meteorological factors affecting the turbulence, it is found that the temperature gradient and wind shear are in good agreement with turbulence strength in both offshore and open ocean areas. Furthermore, the integrated parameters for astronomy and optical telecommunication are derived from profiles over the offshore and open ocean areas. It is of great significance to research the turbulent characteristics of ocean atmosphere for optical transmission and astronomical observations.

Subsurface Ocean Characteristic in the Mentawai Waters during Monsoon Transition Phase on Last 2020

The Indonesia Continental Shelf (LKI) expedition was held during September - October 2020. During the survey, there were ten Conductivity Temperature Depth (CTD) measurement stations that located extending from the west of Mentawai Island to the Indian Ocean. In this study, two-line of subsurface temperature, salinity, and density data were plotted longitudinally. The results show the unique feature between the open ocean and coastal area, the characteristic from open ocean did not affect the characteristic in coastal zone, it is shown from the salinity data. The maximum salinity found in the thermocline layer, between 100-150 m in both of line. The salinity increases from the surface until the thermocline, then slightly decreases to the deep layer. The surface salinity in the coastal area significantly different from the open ocean, it is less than 34 PSU. That is the fact that Wyrtki Jet current did not induce the open ocean water to the coastal water in the subsurface. Otherwise, the temperature and density have a similar pattern with range values around 9-31°C.

Seasonal Variability of Waves Within the Indonesian Seas and Its Relation With the Monsoon Wind

The previous studies have simulated the variability of the wave within the Indonesian seas which showed that the variability of wave follows the seasonal pattern. However, their analysis only consider the influence of local wind forcings. The bias and error of their simulated wave were also unclear. In the present study, we investigate the variability of wave within the Indonesian seas and its relation with the surface wind speed using the combination of reanalysis and remote sensing data with high accuracies. We split the analysis into swell and wind wave to obtain the influence of local and remote wind forcings. We show that at the inner seas (i.e., the South China Sea, Java Sea, Flores Sea, Banda Sea and Arafura Sea), the variability of significant wave height (SWH) is majorly influenced by the variability of the speed of monsoon wind. The maximum SWH during Northwest monsoon (NWM) season is located at the South China Sea while during Southeast monsoon (SEM) season is at Arafura Sea. This indicates that the wind wave (sea) is dominant at the inner seas. At the open seas (i.e., Pacific Ocean and Indian Ocean) the variability of SWH less corresponds to the the speed of monsoon wind. The remote wind forcings control the wave variability in the open ocean area. This indicates that swell is dominant at the open seas. In general, the magnitude of SWHswell is also more than SWHsea within the Indonesian seas.

Recent Trends in SST, Chl‐a, Productivity and Wind Stress in Upwelling and Open Ocean Areas in the Upper Eastern North Atlantic Subtropical Gyre

AbstractThe global upper ocean has been warming during the last decades accompanied with a chlorophyll‐a (Chl‐a) and productivity decrease. Whereas subtropical gyres show similar trends, Eastern Boundary Upwelling Systems are thought to increase in productivity due to increased trade winds. This study analyzes recent trends in sea surface temperature (SST), Chl‐a, net primary production (NPP) and meridional wind stress in the Eastern North Atlantic subtropical gyre (NASE) in order to examine if the global trends can be detected in open ocean and upwelling areas and how the ocean biota responds. Satellite data of such variables of the last 15–40 years were analyzed to calculate mean trends in upwelling areas in the Canary upwelling system and open ocean areas around the Azores, Madeira and the Canary Islands. Our results show significant warming in the area with a maximum of 2.7°C per century for the Azores. Moreover, a general decreasing trend for Chl‐a and NPP seems to be more evident in the permanent upwelling areas, which will be responsible for a loss of 0.13% of the global NPP per century. Our results also highlight a significant expansion of the oceanic desert area of 10% with an increase in unproductive days of up to 84 days in the last 20 years. The competitive relationship of stratification and wind stress in the Canary upwelling system might be a more plausible explanation for the decrease in Chl‐a and NPP in upwelling areas linked to the increase in upwelling favorable wind stress and the surface warming.

Central American mountains inhibit eastern North Pacific seasonal tropical cyclone activity

The eastern North Pacific (ENP) has the highest density of tropical cyclones (TCs) on earth, and yet the controls on TCs, from individual events to seasonal totals, remain poorly understood. One effect that has not been fully considered is the unique geography of the Central American mountains. Although observational studies suggest these mountains can readily fuel individual TCs through dynamical processes, here we show that these mountains indeed play the opposite role on the seasonal timescale, hindering seasonal ENP TC activity by up to 35%. We found that these mountains significantly interrupt the abundant moisture transport from the Caribbean Sea to the ENP, limiting deep convection over the open ocean area where TCs preferentially occur. This study advances our fundamental understanding of ENP TC genesis mechanisms across the weather-to-climate timescales, and also highlights the importance of topography representation in improving the ENP regional climate simulations, as well as TC seasonal predictions and future projections.

Spatial Variation in Pelagic Wildlife Assemblages in the Ascension Island Marine Protected Area: Implications for Monitoring and Management

Bathymetric features such as islands and seamounts, as well as dynamic ocean features such as fronts often harbour rich marine communities. We deployed mid-water baited remote underwater video systems on three expeditions in Ascension Island’s Exclusive Economic Zone (EEZ), surveying the waters associated with six different bathymetric and dynamic ocean features: Ascension Island, two shallow seamounts (summits ≤ 101 m), one deeper seamount (summit > 250 m), apparent fronts, and haphazardly sampled open ocean areas. At Ascension Island, the pelagic assemblage consisted of a moderate proportion of predators and a diverse range of other taxa, including turtles, dolphins, and large non-piscivores. At the two shallow seamounts, sharks, tunas, billfish, and other large pelagic predators formed the vast majority of the assemblage, contributing > 99.9% of biomass and > 86% of abundance. At the deeper seamount, the pelagic community was comparatively depauperate, however the functional composition of its assemblage indicated some similarities to the shallow seamounts. Apparent fronts did not significantly differ from random offshore sites for metrics such as total abundance and taxonomic richness. However, they harboured assemblages with more abundant sharks, tunas, and large piscivores than random ocean open locations and these differences may be driven by certain front-associated species. Our results illustrate that pelagic assemblages vary markedly among different physical and oceanographic features and that seamounts appear particularly important for pelagic predators. The diversity and abundance of the assemblage, as well as the threatened status of many of the species observed, serve to highlight the conservation value of the Ascension Island EEZ. Our results also provide important baseline information of pelagic wildlife assemblages against which the performance of the recently implemented Ascension Island Marine Protected Area can be evaluated.

Rapid Arctic warming and its link to the waviness and strength of the westerly jet stream over West Asia

Rapid sea-ice loss and warming of the Arctic within the past few decades have contributed to changes in the strength and location of midlatitude jet streams. Using ERA-Interim data for the period 1979–2018, warming of the Arctic compared to midlatitudes and its impact on the waviness and strength of the westerly jet stream over West Asia are investigated. Pre- and post-Arctic amplification periods are defined as 1979–1993 and 2004–2018, respectively. Near-surface temperature variability is decreased in the Arctic in the post-Arctic amplification period when a larger area of open ocean has been exposed to the atmosphere. In both pre- and post-Arctic amplification periods, near-surface temperature variabilities in spring and summer were less than half as much of its variability in winter. During the period 1979–2018, both the Arctic and West Asia have warmed, with much higher warming of the Arctic in autumn and winter. Indeed, in contrast to the continental cooling pattern observed in parts of North and Northeast Asia, West Asia has warmed in recent decades. Following a decrease in the meridional temperature gradient, the upper-tropospheric jet stream over West Asia has been reduced in the post-Arctic amplification period in all seasons except autumn. In the post-Arctic amplification period, the zonal wind shear has been also reduced over West Asia in all seasons, while waviness of the Z500 isopleth has been increased in winter. A higher meridional mid-tropospheric waviness is found over the study region (20–75°E) in summer compared to winter because in summer the western part of this region is influenced by a strong subtropical high pressure, while its eastern part is influenced by the Indian monsoon and associated trough of low pressure. • Near-surface temperature variability is decreased in the Arctic in the post-Arctic amplification period • In contrast to cooling of some midlatitude regions, West Asia has warmed in recent decades • Upper-tropospheric jet stream over West Asia has been reduced in the post-Arctic amplification period • Zonal wind shear has been reduced over West Asia in all seasons, but waviness of Z500 isopleth has been increased in winter

GDGTs as indicators for organic-matter sources in a small subtropical river-estuary system

Recently, glycerol dialkyl glycerol tetraethers (GDGTs) have been successfully used to identify different sources for organic-matter in the offshore and open ocean areas, while their applicability in the coastal areas remains unclear. This study was carried out to investigate the behavior of GDGTs and their applicability as indicators for organic-matter sources in a small subtropical river-estuary system, the Jiulong River-Estuary system (JRES), southeastern China. In 2018, three groups of samples including riverbank soils, riverbed surface sediments, and estuarine surface sediments were collected and analyzed. The results supported three main findings: 1) The abundances of GDGTs and crenarchaeol, and the ratios of iGDGTs/bGDGTs, GDGT-0/crenarchaeol (GDGT-0/cren), crenarchaeol isomer / (crenarchaeol + crenarchaeol isomer) and the IIIa/IIa, were good indicators for organic-matter sources; 2) At the middle and lower reaches of West River, the abnormally high values of GDGT-0/cren ratio and bGDGT abundance might indicate anthropogenic-induced water eutrophication; and 3) The branched and isoprenoid tetraether index (BIT) was especially sensitive in indicating of the soil- vs marine-organic matter contribution to the total organic matter of estuarine sediments. The high BIT values at the estuary turbidity maximum zone (TMZ) and the mid estuary suggested that TMZ filtering effect, preservation conditions and extra sources of soils have impacted the organic-matter distribution. Understanding the behavior and application of GDGTs in such a system helps to improve research on organic carbon cycling in the coastal system.

Humpback whale abundance south of 60°S from three complete circumpolar sets of surveys

Austral summer estimates of abundance are obtained for humpback whales (Megaptera novaeangliae) in the Southern Ocean from the IWC’s IDCR and SOWER circumpolar programmes. These surveys have encircled the Antarctic three times: 1978/79–1983/84 (CPI), 1985/86–1990/91 (CPII) and 1991/92–2003/04 (CPIII), criss-crossing strata totalling respectively 64.3%, 79.5% and 99.7% of the open-ocean area south of 60°S. Humpback whales were absent from the Ross Sea, but were sighted in all other regions, and in particularly high densities around the Antarctic Peninsula, in Management Area IV and north of the Ross Sea. Abundance estimates are presented for each CP, for Management Areas, and for assumed summer feeding regions of each Breeding Stock. Abundance estimates are negatively biased because some whales on the trackline are missed and because some humpback whales are outside the survey region. Circumpolar estimates with approximate midpoints of 1980/81, 1987/88 and 1997/98 are 7,100 (CV = 0.36), 10,200 (CV = 0.30) and 41,500 (CV = 0.11). When these are adjusted simply for unsurveyed northern areas, the estimated annual rate of increase is 9.6% (95% CI 5.8–13.4%). All Breeding Stocks are estimated to be increasing but increase rates are significantly greater than zero only for those on the eastern and western coasts of Australia. Given the observed rates of increase, the current total Southern Hemisphere abundance is greater than 55,000, which is similar to the summed northern breeding ground estimates (~60,000 from 1999–2008). Some breeding ground abundance estimates are far greater, and others far lower, than the corresponding IDCR/SOWER estimates, in a pattern apparently related to the latitudinal position of the Antarctic Polar Front.

Impacts of climate changes on the phytoplankton biomass of the Indonesian Maritime Continent

We used more than two decades (1997–2019) of satellite-estimated phytoplankton chlorophyll-a concentration (Chl-a) during September–December time intervals to discern the spatial and temporal changes of phytoplankton biomass in the Indonesian Maritime Continent (IMC) associated with different climatic events. In the IMC coastal areas (except for the northern Malacca Strait) climate changes influenced Chl-a by varying rainfall/river discharge. Chl-a declined most notably during concurrent positive Indian Ocean Dipole (IOD) and El Niño events, whereas they increased most notably during concurrent negative IOD and La Niña events. In the open ocean areas of the IMC, climate changes influenced Chl-a by varying the occurrence of upwelling and downwelling. The dominant climate mode determining Chl-a shifted from the IOD in the eastern Indian Ocean to the El Niño/Southern Oscillation (ENSO) in the western Pacific Ocean. In the eastern Indian Ocean, the impact of the IOD on Chl-a was more than one order of magnitude greater than the impact of ENSO. The results implied that low-trophic-level marine organisms such as phytoplankton, high-trophic-level marine organisms such as fish, and biogeochemical cycles in the eastern Indian Ocean of the IMC may all be more affected by the IOD than by the ENSO.

Azorean demersal longline survey abundance estimates: Procedures and variability

Survey data from the Azores is used for fisheries stock assessments under the ICES Working Group on the Biology and Assessment of Deep-sea Fisheries Resources (WGDEEP) covering deep open ocean areas. The Azores research cruise using bottom longlines for abundance estimation is probably unique in the Northeast Atlantic Ocean. This study analyzed data from annual Azorean bottom longline surveys (ICES subdivision 10a2) from 1996 to 2018 to calculate abundance indices of commercial demersal species, to estimate the statistical significance of the annual changes in the abundance estimates, and to examine the possible factors that cause this variability. The catch rates of these surveys appear to provide accurate indices of abundance for most of the commercially important demersal species. The observed inter-annual variability of the survey abundance estimates can be explained by survey effort distribution, fishery dynamics, aggregation patterns of some species, habitat preferences, fish movements, and environmental effects. However, other factors can affect these estimates (soak time, gear saturation and competition for hooks) and we recommend that additional studies be undertaken to understand these effects.

Less climatic resilience in the Arctic

Twenty years ago the Arctic system was more resilient than now as sea ice was three times thicker than today. Heavier and more persistent sea ice provided a buffer against the influence of short-term climate fluctuations. Such recent increases in sea ice/atmospheric interactions lead to revisiting the concept of abrupt change. The Arctic climate is stabilized by a negative radiative feedback, as increased temperatures of the surface and atmospheric lose more long wave energy. However, through new shifts in albedo feedback, open ocean areas are absorbing more of the incoming solar heat. Recent multi-year environmental extremes, potential albedo instabilities, and increased sensitivity of sea ice to storms in marginal seas, are overcoming negative radiative feedback, which point to passing impending climatic and ecosystem thresholds. Unless CO2 emissions are reduced, further Arctic extremes are expected in the next decades with environmental and societal impacts spreading through the Arctic and beyond.

Impacts of the unique landfall Typhoons Damrey on chlorophyll-a in the Yellow Sea off Jiangsu Province, China

Typhoon Damrey was the rare typhoon to make a straight landfall in northern Jiangsu Province (35°N), China. The unique influence of typhoon Damrey and the following typhoons Haikui on the phytoplankton bloom and related dynamic mechanisms were fully investigated. Because of the complex regional features, e.g., nutrient distribution, stratification and sediment concentration, it induced different responses to the ocean along its track. In the near shore region, the Chlorophyll-a (Chl_a) concentration dropped prominently during typhoon, associating with strong wind events, because of the onshore advection of water with a low amount of Chl_a and coastal downwelling. For the shelf regions, no significant blooms were identified and the Chl_a values after typhoon were less than the preceding maximum values. Although a large amount of mixing happened in the water column, insufficient sunshine for photosynthesis caused by a high suspended sediment concentration (SSC) (10.8 g m−3) near the shore and a lack of nutrients in the bottom boundary of the open sea resulted in no Chl_a bloom in these two areas. For the open ocean area off the Yangtze River estuary, where subsurface nitrate concentration was high, the formation of a Chl_a bloom after strong winds was mainly determined by the intensity of the stratification in the upper ocean. The enhancement of nutrients from the subsurface layer became stronger (weaker) when the pycnocline was weakened (strengthened). As the pycnocline and stratification weakened, the Chl_a concentration was significantly higher than that on August 7 because of the intensified upward transport of nutrients from the deep layer. This study offers a comparison of the different mechanisms by which typhoons can impact Chl_a in mid-latitude regions and will be helpful for evaluating typhoon-induced biological responses in future.

First abundance estimate for white whales Delphinapterus leucas in Svalbard, Norway

The Svalbard Archipelago (Norway) is experiencing rapid declines in the seasonal duration and extent of sea-ice cover, and local tidewater glaciers are melting. These environmental changes represent a threat to ice-associated species in the region, including white whales Delphinapterus leucas. However, no estimates of stock size or trends are available for this stock. An aerial survey was conducted during the summer of 2018, covering the coastlines of all major islands in Svalbard, as well fjords and open ocean areas. A total count was attempted for the coastlines, while coverage of the fjords and open ocean areas was designed as distance-sampling line transects. In total, 265 white whales were detected in 22 groups along the 4965 km of coastline coverage. No whales were observed on fjord (1481 km) or open ocean transects (535 km). After correcting for surface availability using behavioural data from the same area (in summer) and making adjustments for small areas not flown during the survey, the stock size was estimated to be 549 individuals (95% CI: 436%%CONV_ERR%%723). This estimate is surprisingly low given that this species is one of the most frequently observed cetaceans in the area, but it confirms suspicions based on difficulties in finding animals when operating white whale tagging programmes over the past decade. This first population estimate is important in the context of the rapid environmental change taking place in the Arctic and for providing a baseline for comparison with future estimates.

Projecting global mariculture diversity under climate change.

Previous studies have focused on changes in the geographical distribution of terrestrial biomes and species targeted by marine capture fisheries due to climate change impacts. Given mariculture's substantial contribution to global seafood production and its growing significance in recent decades, it is essential to evaluate the effects of climate change on mariculture and their socio‐economic consequences. Here, we projected climate change impacts on the marine aquaculture diversity for 85 of the currently most commonly farmed fish and invertebrate species in the world's coastal and/or open ocean areas. Results of ensemble projections from three Earth system models and three species distribution models show that climate change may lead to a substantial redistribution of mariculture species richness potential, with an average of 10%–40% decline in the number of species being potentially suitable to be farmed in tropical to subtropical regions. In contrast, mariculture species richness potential is projected to increase by about 40% at higher latitudes under the ‘no mitigation policy’ scenario (RCP 8.5) by the mid‐21st century. In Exclusive Economic Zones where mariculture is currently undertaken, we projected an average future decline of 1.3% and 5% in mariculture species richness potential under RCP 2.6 (‘strong mitigation’) and RCP 8.5 scenarios, respectively, by the 2050s relative to the 2000s. Our findings highlight the opportunities and challenges for climate adaptation in the mariculture sector through the redistribution of farmed species and expansion of mariculture locations. Our results can help inform adaptation planning and governance mechanisms to minimize local environmental impacts and potential conflicts with other marine and coastal sectors in the future.

Enhancement of phytoplankton biomass leeward of Tahiti as observed by Biogeochemical-Argo floats

Abstract The South Pacific Subtropical Gyre (SPSG) is a vast and remote oceanic system where the variability in phytoplankton biomass and production is still largely uncertain due to the lack of in situ biogeochemical observations. The SPSG is an oligotrophic environment where the ecosystem is controlled predominantly by nutrient depletion in surface waters. However, this dynamic is altered in the vicinity of islands where increased biological activity occurs (i.e. the island mass effect, IME). This study mainly focuses on in situ observations which show evidence of an IME leeward of Tahiti (17.7°S - 149.5°W), French Polynesia. Physical and biogeochemical observations collected with two Biogeochemical-Argo profiling floats are used to investigate the dynamics of phytoplankton biomass. Data from the first float, drifting from April 2015 to November 2016 over >1000 km westward of Tahiti, describe the open ocean conditions. The second float, deployed leeward of Tahiti in October 2015, stayed within 45 km off Tahiti for three months before it stopped communicating. In the oligotrophic central SPSG, our observations show that the deepening of the deep chlorophyll maximum (DCM) from winter to summer is light-driven and that the wintertime increase in chlorophyll a concentration in the upper layer is likely to be due to the process of photoacclimation, consistent with previous observations in oligotrophic environments. In contrast, leeward of Tahiti, the DCM widens toward the surface during late spring in association with a biological enhancement in the upper layer. Using Biogeochemical-Argo data, meteorological data from Tahiti, Hybrid Coordinate Ocean Model outputs and satellite-derived products (i.e., horizontal currents and associated fronts), the physical mechanisms involved in producing this biological enhancement leeward of Tahiti have been investigated. The IME occurs during a period of strong precipitation and in a zone of weak currents downstream of the island. We conjecture that the land drainage induces a significant supply of nitrate in the ocean upper layer (down to ~100 m) while a zone of weak currents in the southwestern zone behind Tahiti allows an accumulation zone to form, hence increasing phytoplankton growth up to 20 km away from the coastlines. A bio-optical-based community index suggests that the composition of the phytoplankton community differs leeward of Tahiti from that in the open ocean area, with more microphytoplankton within the IME, which is associated with an increase in the carbon export to the deeper ocean.

Sinking of Gelatinous Zooplankton Biomass Increases Deep Carbon Transfer Efficiency Globally

AbstractGelatinous zooplankton (Cnidaria, Ctenophora, and Urochordata, namely, Thaliacea) are ubiquitous members of plankton communities linking primary production to higher trophic levels and the deep ocean by serving as food and transferring “jelly‐carbon” (jelly‐C) upon bloom collapse. Global biomass within the upper 200 m reaches 0.038 Pg C, which, with a 2–12 months life span, serves as the lower limit for annual jelly‐C production. Using over 90,000 data points from 1934 to 2011 from the Jellyfish Database Initiative as an indication of global biomass (JeDI: http://jedi.nceas.ucsb.edu, http://www.bco‐dmo.org/dataset/526852), upper ocean jelly‐C biomass and production estimates, organism vertical migration, jelly‐C sinking rates, and water column temperature profiles from GLODAPv2, we quantitatively estimate jelly‐C transfer efficiency based on Longhurst Provinces. From the upper 200 m production estimate of 0.038 Pg C year−1, 59–72% reaches 500 m, 46–54% reaches 1,000 m, 43–48% reaches 2,000 m, 32–40% reaches 3,000 m, and 25–33% reaches 4,500 m. This translates into ~0.03, 0.02, 0.01, and 0.01 Pg C year−1, transferred down to 500, 1,000, 2,000, and 4,500 m, respectively. Jelly‐C fluxes and transfer efficiencies can occasionally exceed phytodetrital‐based sediment trap estimates in localized open ocean and continental shelves areas under large gelatinous blooms or jelly‐C mass deposition events, but this remains ephemeral and transient in nature. This transfer of fast and permanently exported carbon reaching the ocean interior via jelly‐C constitutes an important component of the global biological soft‐tissue pump, and should be addressed in ocean biogeochemical models, in particular, at the local and regional scale.

Transition from eyeball to snowball driven by sea-ice drift on tidally locked terrestrial planets

Tidally locked terrestrial planets around low-mass stars are the prime targets for future atmospheric characterizations of potentially habitable systems, especially the three nearby ones--Proxima b, TRAPPIST-1e, and LHS 1140b. Previous studies suggest that if these planets have surface ocean they would be in an eyeball-like climate state: ice-free in the vicinity of the substellar point and ice-covered in the rest regions. However, an important component of the climate system--sea ice dynamics has not been well studied in previous studies. A fundamental question is: would the open ocean be stable against a globally ice-covered snowball state? Here we show that sea-ice drift cools the ocean's surface when the ice flows to the warmer substellar region and melts through absorbing heat from the ocean and the overlying air. As a result, the open ocean shrinks and can even disappear when atmospheric greenhouse gases are not much more abundant than on Earth, turning the planet into a snowball state. This occurs for both synchronous rotation and spin-orbit resonances (such as 3 to 2). These results suggest that sea-ice drift strongly reduces the open ocean area and can significantly impact the habitability of tidally locked planets.

Using historical fisheries data to predict tuna distribution within the British Indian Ocean Territory Marine Protected Area, and implications for its management

Abstract Recently, several large marine protected areas (MPAs) have been established globally, and it is hoped that they will aid the recovery of populations of highly mobile, large pelagic species. Understanding the distribution of these species within MPAs is key to delivering effective management, but monitoring can be challenging over such vast areas of open ocean. Historical fisheries data, collected prior to MPA establishment, can provide an insight into the past distributions of target species. We investigated the spatial and temporal distribution of yellowfin (Thunnus albacares) and skipjack (Katsuwonus pelamis) tuna catch using logbook data from the purse seine fishery in the British Indian Ocean Territory from 1996 to 2010, before it was established as an MPA in April 2010. Generalized additive models were used to predict tuna presence and relative abundance from fishing records in relation to temporal and environmental variables. Significant variables included sea salinity, temperature, and water velocity. Predictions from the models identified a distinct hotspot for large yellowfin tuna within the MPA, and areas of high predicted relative abundance of skipjack tuna. We recommend that these areas are used as focal points from which populations can be monitored and investigations into tuna residency time can occur, so that the effectiveness of the MPA in conserving highly mobile pelagic fish can be determined.

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.