Guilherme Augusto Bortolotto

Antarctica’s ice shelves play a critical role in modulating ice loss to the ocean by buttressing grounded ice upstream. With the potential to impact ice-shelf stability, persistent polynyas (open-water areas surrounded by sea ice that occur across multiple years at the same location) at the edge of many ice-shelf fronts, are maintained by winds and/or ocean heat and are locations of strong ice-ocean-atmosphere interactions. However, in situ observations of polynyas are sparse due to the logistical constraints of collecting Antarctic field measurements. Here, we used wintertime (May–August) temperature and salinity observations derived from seal-borne instruments deployed in 2014, 2019, and 2020, in conjunction with thermal imagery from the MODerate resolution Imaging Spectroradiometer (MODIS) and the Landsat 8 Thermal Infrared Sensor (TIRS) to investigate spatial, temporal, and thermal structural variability of polynyas near Pine Island Glacier (PIG). Across the three winters considered, there were 176 anomalously warm (>3σ from background) seal dives near the PIG ice front, including 26 dives that coincided with MODIS images with minimal cloud cover that also showed a warm surface temperature anomaly. These warm surface temperatures correlated with ocean temperatures down to 150 m depth or deeper, depending on the year, suggesting that MODIS-derived surface thermal anomalies can be used for monitoring polynya presence and structure during polar night. The finer spatial resolution (100 m) of TIRS wintertime thermal imagery captures more detailed thermal structural variability within these polynyas, which may provide year-round insight into sub-ice-shelf processes if this dataset is collected operationally.

West Antarctic ice-shelf thinning is primarily caused by ocean-driven basal melting. Here we assess ocean variability below Thwaites Eastern Ice Shelf (TEIS) and reveal the importance of local ocean circulation and sea-ice. Measurements obtained from two sub-ice-shelf moorings, spanning January 2020 to March 2021, show warming of the ice-shelf cavity and an increase in meltwater fraction of the upper sub-ice layer. Combined with ocean modelling results, our observations suggest that meltwater from Pine Island Ice Shelf feeds into the TEIS cavity, adding to horizontal heat transport there. We propose that a weakening of the Pine Island Bay gyre caused by prolonged sea-ice cover from April 2020 to March 2021 allowed meltwater-enriched waters to enter the TEIS cavity, which increased the temperature of the upper layer. Our study highlights the sensitivity of ocean circulation beneath ice shelves to local atmosphere-sea-ice-ocean forcing in neighbouring open oceans.

Antarctic ice-shelves melting is accelerating, and the highest rates for the continent are observed in the Amundsen Sea, where Weddell seals are understudied. By modelling an unrivalled telemetry tracking dataset, we show that this top predator in the area is more likely found in shallower waters, closer to the coast, half-covered by ice and where the temperature at the ocean bottom is around 0.5°C or colder. Their distribution during winter is more restricted to coastal areas in the eastern Amundsen Sea and spread out in warmer months. That fluctuation reflects the drastic variation in their habitat illustrating their potential sensitivity to the upcoming impacts of climate changes. We discuss their overlap with Antarctic toothfish fisheries in the area and the potential consequences of global warming to the ecology of the seals.

Franciscana dolphins in Babitonga Bay represent the only population of that critically endangered species which is confined to an estuary. Surrounded by large cities and harbors, that environment presents intense human activities and potential impacts that may threaten the dolphins. Understanding their habitat use and distribution can inform mitigation of such impacts. Here we used acoustic data from sixty fixed passive acoustic monitoring stations, implemented between June and December 2018. The relationship between the occurrence of franciscanas and environmental variables was investigated with generalized additive mixed models. The selected model presented 51% of explained deviance and included “time of day”, “intensity of presence of Guiana dolphins”, “maximum slope”, and “bottom sediment”, among other less statistically significant variables. A daily distribution pattern was identified, with franciscanas remaining in the areas of greatest occurrence especially in the morning and seemed to prefer sandy bottom and flatter areas. Areas intensively used by Guyana dolphins were avoided. Additionally, we mapped their distribution using “Empirical Bayesian Kriging” to identify the main areas of occurrence and for foraging. Franciscanas are consistently predominant in the innermost region of the estuary, without expressive use of the entrance channel, but with a wider range in winter than in the spring. The area around the islands, between the north and south banks, represents an important foraging area, a behavior more frequent during dawn and night. This study provides important insights into critical habitat and behavioral patterns of franciscanas, especially this critically endangered population.

After decades of population growth, the central stock of the North Pacific population of humpback whales, known as the Hawai’i Distinct Population Segment (HDPS), was delisted from its endangered status in 2016. At that time, however, an unprecedented heating event, the “Pacific Marine Heatwave” (PMH) was already underway. The PMH coincided with reports of major declines of sightings of humpback whales, including calves of the year, on both the Hawaiian wintering grounds and the feeding grounds of Southeast Alaska. To examine the resiliency of the Hawai’i Distinct Population Segment, we conducted aerial surveys of the high-density Maui Nui region immediately following the PMH event in 2019 and 2020, using distance sampling methods identical to those used in an earlier series (1993 to 2003). Results showed whale densities at or above those seen earlier, with mean density for 2020 highest overall. Crude birth rates (% groups containing a calf) were similarly comparable to those recorded in the earlier series, with an increase from 2019 to 2020. Overall, results suggest the central North Pacific humpback whale population stock to be resilient in the face of this major climatic event.

Suckerfish attached to dolphin species have been extensively reported worldwide, yet such association has been rarely seen in the tropical and shallow waters of South America. In Brazil, the Guiana dolphin Sotalia guianensis is distributed along almost the entire extent of the coast and only one case of association with suckerfish has been published. Here we report on a sharksucker Echeneis naucrates associated with a young Guiana dolphin on the north-eastern coast of Brazil. The juvenile dolphin with an attached sharksucker was observed on two occasions separated by a 47-day period; we hypothesize the occurrence of host attachment fidelity. The present report adds information to better discuss the ecological interactions between echeneids and dolphins, and expands the baseline information on cetacean species serving as host to suckerfish.