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Abstract Passive acoustic monitoring was used to detect the sounds of rarely sighted Antarctic blue and fin whales to investigate their seasonal occurrence (as presence or absence of whale calls) and behaviour (as determined from call rates) in the Benguela ecosystem. Data were collected using autonomous acoustic recorders deployed on oceanographic moorings for 16.26 months off the west coast of South Africa in 2014 and 2015. Satellite derived environmental variables were used as predictors of whale acoustic occurrence and behaviour. Migratory Antarctic blue and fin whales were acoustically present in South African waters between May and August with call occurrence peaks in July whereas some fin whales extended their presence to November. No whale calls were recorded in summer for either species, suggesting whales use the Benguela ecosystem as an overwintering ground and migration route. Antarctic blue whales produced both their characteristic Z -call and their feeding associated D-call. Fin whales produced calls characteristic of animals from the eastern Antarctic fin whale acoustic population. Random forest models identified environmental variables such as sea surface temperature anomaly, sea surface height, wind speed, months of the year, Ekman upwelling index and log-transformed chlorophyll-a as the most important predictors of call occurrence and call rates of blue and fin whales. Here we present the first acoustic recordings of Antarctic blue and fin whales in the Benguela ecosystem, and provide preliminary information to investigate seasonal abundance and distribution of these large baleen whale populations. This work demonstrates the feasibility of cost-effectively monitoring Antarctic top-consumer baleen whales in the Benguela ecosystem. Highlights • Whale calls were detected from May to November but peaked in July. • First acoustic records of sympatric whale occurrence off the west coast of South Africa. • Acoustic evidence of Antarctic blue whales feeding in the Benguela ecosystem • Call occurrences indicate the west coast of South Africa as an overwintering ground and migration route. • Environmental conditions influenced whale call occurrence and diel acoustic behaviour. [ABSTRACT FROM AUTHOR]

The Prince Edward Islands (PEIs) lie within the Antarctic Circumpolar Current (ACC), in a transition zone bordered by the sub‐Antarctic Front (SAF) to the north and the Antarctic Polar Front (APF) in the south. A climate‐driven southward shift of the ACC and its frontal systems, the SAF and APF, in the vicinity of the PEIs is associated with a long‐term decline in the frequency of island‐associated phytoplankton blooms. These oceanographic perturbations coincide with significant declines in top predator populations attributed to shifts in the distribution and availability of prey, illustrating the interconnectedness between the marine and terrestrial ecosystems of the PEIs. This study investigated the influence of oceanographic variability on the marine ecosystem of the PEIs. A shift in phytoplankton and bacterial communities was observed that coincides with the position of the southern branch of the SAF, which was located to the north of the PEIs during 2014 and to the south during 2012, 2013, and 2015. These shifts in the diversity and structure of marine microbial communities correlate with significant perturbations in the position of the SAF relative to the islands leading us to conlclude that bacterial and phytoplankton communities in the PEI region are strongly influenced by shifts in the position of the SAF relative to the PEIs. This study highlights the critical need to link on‐going physical time series measurements with biological observations to provide a better understanding of the direct role that the upstream dynamics has on the near‐shore island environment and its productivity. [ABSTRACT FROM AUTHOR]

The European Water Framework Directive has been adopted by Member States to assess and manage the ecological integrity of surface waters. Specific challenges include harmonizing diverse assessment systems across Europe, linking ecological assessment to restoration measures and reaching a common view on ‘good’ ecological status. In this study, nine national macrophyte-based approaches for assessing ecological status were compared and harmonized, using a large dataset of 539 European lakes. A macrophyte common metric, representing the average standardized view of each lake by all countries, was used to compare national methods. This was also shown to reflect the total phosphorus (r 2  = 0.32), total nitrogen (r 2  = 0.22) as well as chlorophyll- a (r 2  = 0.35–0.38) gradients, providing a link between ecological data, stressors and management decisions. Despite differing assessment approaches and initial differences in classification, a consensus was reached on how type-specific macrophyte assemblages change across the ecological status gradient and where ecological status boundaries should lie. A marked decline in submerged vegetation, especially Charophyta (characterizing ‘good’ status), and an increase in abundance of free-floating plants (characterizing ‘less than good’ status) were the most significant changes along the ecological status gradient. Macrophyte communities of ‘good’ status lakes were diverse with many charophytes and several Potamogeton species. A large number of taxa occurred across the entire gradient, but only a minority dominated at ‘less than good’ status, including filamentous algae, lemnids, nymphaeids, and several elodeids (e.g., Zannichellia palustris and Elodea nuttallii ). Our findings establish a ‘guiding image’ of the macrophyte community at ‘good’ ecological status in hard-water lakes of the Central-Baltic region of Europe. [ABSTRACT FROM AUTHOR]

We present here sea surface salinity (SSS) and temperature (SST) data collected on board the S.A. Agulhas-I and S.A. Agulhas-II research vessels, in the framework of the South African National Antarctic Programme (SANAP). Onboard Sea-Bird thermosalinographs were regularly calibrated and continuously monitored in-between cruises, and no appreciable sensor drift emerged. Water samples were taken on a daily basis and later analyzed with a Portasal salinometer; some CTD measurements collected along the cruises were used to validate the data. No systematic differences appeared after a rigorous quality control on continuous data. Results show that salinity measurement error was a few hundredths of a unit on the practical salinity scale. Quality control included several steps, among which an automatic detection of unreliable values through selected threshold criteria and an attribution of quality flags based on multiple criteria, i.e., analysis of information included in the cruise reports, detection of insufficient flow and/or presence of air bubbles and ice crystals in the seawater pipe, visual inspection of individual campaigns, and ex post check of sea ice maps for confirming ice field locations. This data processing led us to discard about 36% of acquired observations, while reliable data showed an excellent agreement with several independent SSS products. Nevertheless, a sea ice flag has been included for identifying valid data which could have been affected by scattered sea ice contamination. In our opinion, this dataset, available through an unrestricted repository at https://doi.org/10.7289/V56M3545, contributes to improving the knowledge of surface water features in one of the most important regions for global climate. The dataset will be highly valuable for studies focusing on climate variability in the Atlantic sector of the Southern Ocean, especially across the Antarctic Circumpolar Current and its fronts. Furthermore, we expect that the collected SSS data will represent a valuable tool for the calibration and validation of recent satellite observations provided by SMOS and Aquarius missions. [ABSTRACT FROM AUTHOR]

Six years of simultaneous moored observations near the western and eastern boundaries of the South Atlantic are combined with satellite winds to produce a daily time series of the basin-wide meridional overturning circulation (MOC) volume transport at 34.5°S. The results demonstrate that barotropic and baroclinic signals at both boundaries cause significant transport variations, and as such must be concurrently observed. The data, spanning ~20months during 2009-2010 and ~4 years during 2013-2017, reveal a highly energetic MOC record with a temporal standard deviation of 8.3 Sv, and strong variations at time scales ranging from a few days to years (peak-to-peak range = 54.6 Sv). Seasonal transport variations are found to have both semiannual (baroclinic) and annual (Ekman and barotropic) timescales. Interannual MOC variations result from both barotropic and baroclinic changes, with density profile changes at the eastern boundary having the largest impact on the year-to-year variations. [ABSTRACT FROM AUTHOR]

The Water Framework Directive is the first international legislation to require European countries to establish comparable ecological assessment schemes for their freshwaters. A key element in harmonising quality classification within and between Europe's river basins is an “Intercalibration” exercise, stipulated by the WFD, to ensure that the good status boundaries in all of the biological assessment methods correspond to similar levels of anthropogenic pressure. In this article, we provide a comprehensive overview of this international comparison, focusing on the assessment schemes developed for freshwater lakes. Out of 82 lake ecological assessment methods reported for the comparison, 62 were successfully intercalibrated and included in the EC Decision on intercalibration, with a high proportion of phytoplankton (18), macrophyte (17) and benthic fauna (13) assessment methods. All the lake assessment methods are reviewed in this article, including the results of intercalibration. Furthermore, the current gaps and way forward to reach consistent management objectives for European lakes are discussed. [ABSTRACT FROM AUTHOR]

In this paper we analyze a long-term dataset on the recovery from eutrophication of Lake Veluwe (The Netherlands). Clear hysteresis was observed in a number of ecosystem variables: the route to recovery differed significantly from the route that led to loss of clear water. The macrophyte dominated state disappeared in the late 1960s at TP above 0.20 mg l−1, whereas its return occurred at less than 0.10 mg TP l−1. Several regime shifts resulting in the occurrence of three alternative stable states were observed over a period of 30 years. The turbid state showed resistance to change, despite a strong and prompt reduction in Chl -a following reduction of external P-loading. The most important component that determined hysteresis in the return to clear water was not internal P-loading, but a high level of nonalgal light attenuation (through sediment resuspension) maintained by the interaction between wind and benthivorous fish. Although Chara was able to re-colonize the most shallow parts of the lake, recovery stalled and for a number of years clear (above charophyte beds) and turbid (deeper parts of the lake) water co-existed, as a separate alternative state on route to full recovery. Lake-wide clear water was re-established after bream density had been reduced substantially. This allowed a return of zebra mussels to the lake, whose high filtration capacity helped in maintaining clear water. In this study, we were able to identify the main drivers of hysteresis and regime shifts, although formal demonstration of cause and effect was not possible on the basis of field data alone. We argue that resilience of the present clear water state of Lake Veluwe very much depends on sizable populations of a few keystone species, especially Chara (stoneworts) and Dreissena (zebra mussels), and that careful management of these species is equally important as control of nutrients. Lake management should strive to maintain and strengthen resilience of the ecosystem, and this should offer protection against a renewed collapse of the clear state. [ABSTRACT FROM AUTHOR]

The fish community in the shallow Lake Veluwe (3400 ha) has recently changed in composition. The total biomass of fish decreased to ca. 35% of the original biomass. The change in fish biomass followed the introduction of a commercial fishery and was in its turn followed by a rapid expansion of macrophyte beds dominated by Chara aspera Deth. ex Willd.An individual-based fish model was used to evaluate the causation of these events. We estimated natural mortality of the bream population (Abramis brama L.) using data on growth, recruitment and size distribution. The model predicted that without the fishery the biomass of the bream population would hardly change and that the fishery could explain the change in the biomass and size composition.The rapid expansion of C. aspera was unlikely without the fishery, as Chara needs transparency down to the bottom and undisturbed sediment. The reduction of the bream population created favourable conditions for zebra mussels Dreissena polymorpha (Pallas) to settle which in turn created the clear water, necessary for the development of the Chara beds. [Copyright &y& Elsevier]

Knowledge on the occurrence and behaviour of baleen whales around sub-Antarctic regions is limited, and usually based on short, seasonal sighting research from shore or research vessels and whaling records, neither of which provide accurate and comprehensive year-round perspectives of these animals' ecology. We investigated the seasonal acoustic occurrence and diel vocalizing pattern of baleen whales around the sub-Antarctic Prince Edward Islands (PEIs) using passive acoustic monitoring data from mid-2021 to mid-2023, detecting six distinct baleen whale songs from Antarctic blue whales, Madagascan pygmy blue whales, fin whales, Antarctic minke whales, humpback whales, and sei whales. Antarctic blue and fin whales were detected year-round whereas the other species' songs were detected seasonally, including a new Antarctic minke whale bio-duck song sub-type described here for the first time. Antarctic minke and sei whales were more vocally active at night-time whereas the other species had no clear diel vocalizing patterns. Random forest models identified month and/or sea surface temperature as the most important predictors of all baleen whale acoustic occurrence. These novel results highlight the PEIs as a useful habitat for baleen whales given the number of species that inhabit or transit through this region., (© 2024. The Author(s).)

The characteristics of aviation-induced aerosol, its processing, and effects on cirrus clouds and climate are still associated with large uncertainties. Properties of aviation-induced aerosol, however, are crucially needed for the assessment of aviation's climate impacts today and in the future. We identified more than 1100 aircraft plume encounters during passenger aircraft flights of the IAGOS-CARIBIC Flying Laboratory from July 2018 to March 2020. The aerosol properties inside aircraft plumes were similar, independent of the altitude (i.e., upper troposphere, tropopause region, and lowermost stratosphere). The exhaust aerosol was found to be mostly externally mixed compared to the internally mixed background aerosol, even at a plume age of 1 to 3 h. No enhancement of accumulation mode particles (diameter >250 nm) could be detected inside the aircraft plumes. Particle number emission indices (EIs) deduced from the observations in aged plumes are in the same range as values reported from engine certifications. This finding, together with the observed external mixing state inside the plumes, indicates that the aviation exhaust aerosol almost remains in its emission state during plume expansion. It also reveals that the particle number EIs used in global models are within the range of the EIs measured in aged plumes.

Killer whales are apex predators with temporally and spatially varying distributions throughout the world's oceans. Their ecology and behaviour are poorly understood in most regions due to limited research, often because of logistical challenges. Here, we used a passive acoustic monitoring device to investigate the seasonal acoustic occurrence and diel vocalizing behaviour of killer whales around the remote sub-Antarctic Prince Edward Islands (PEIs), Southern Ocean. Killer whales showed diel vocalizing patterns that varied seasonally in relation to their prey abundance and social activities. Killer whale calls were intermittently detected year-round with a high number of hours containing calls in October to December, and a secondary peak in February to May, corresponding to seal prey abundance. Random forest modelling identified wind speed as the primary predictor of the occurrence of killer whale calls (with a negative correlation) while sea surface height, chlorophyll-a and sea surface temperature were moderately important. We provide the first acoustic evidence that killer whale occurrence around the PEIs might coincide with variability in environmental conditions and prey abundance. Our results provide the first indication of diel vocalizing pattern of killer whales in the Southern Ocean. This knowledge is important for understanding killer whale ecology and adaptation to the changing oceans., Competing Interests: The authors have no competing interests., (© 2024 The Authors.)

The concept of "reference conditions" describes the benchmark against which current conditions are compared when assessing the status of water bodies. In this paper we focus on the establishment of reference conditions for European lakes according to a phytoplankton biomass indicator--the concentration of chlorophyll-a. A mostly spatial approach (selection of existing lakes with no or minor human impact) was used to set the reference conditions for chlorophyll-a values, supplemented by historical data, paleolimnological investigations and modelling. The work resulted in definition of reference conditions and the boundary between "high" and "good" status for 15 main lake types and five ecoregions of Europe: Alpine, Atlantic, Central/Baltic, Mediterranean, and Northern. Additionally, empirical models were developed for estimating site-specific reference chlorophyll-a concentrations from a set of potential predictor variables. The results were recently formulated into the EU legislation, marking the first attempt in international water policy to move from chemical quality standards to ecological quality targets.