Alfred Wegener Institute for Polar and Marine Research
Electronic Publication Information CenterNot a member yet
52828 research outputs found
Sort by
Decadal change in deep-ocean dissolved oxygen in the North Atlantic Ocean and North Pacific Ocean
Get PDFDeclining dissolved oxygen concentrations are documented at upper and mid ocean depths, but less is known about the deep ocean. Long time-series measurements of dissolved oxygen analyzed with Winkler titration over several decades reveal regional differences at six stations in the abyssal North Atlantic Ocean and North Pacific Ocean. A significant decline in dissolved oxygen was evident at two stations in the northeast Pacific Ocean at 4000–4200 m depth (Stations PAPA and M). A similar decreasing but insignificant trend was recorded in the Arctic region of the North Atlantic Ocean (HAUSGARTEN). However, there was no significant decrease in dissolved oxygen at two temperate stations in the North Atlantic Ocean (PAP, BATS) and at one tropical station in the central North Pacific Ocean (ALOHA) all at similar depths >4000 m over similar time periods. Continued long time-series observations will be needed to monitor global deep ocean processes and the impact of changing climate. We compare these rare long-term observations with model estimations from historical (1850–2014) and projected (2015–2100) forcing under a continued high greenhouse gas emission scenario
Global mean sea level over the past 4.5 million years.
Get PDFChanges in global mean sea level (GMSL) during the late Cenozoic remain uncertain. We use a reconstruction of changes in δ18O of seawater to reconstruct GMSL since 4.5 million years ago (Ma) that accounts for temperature-driven changes in the δ18O of global ice sheets. Between 4.5 and 3 Ma, sea level highstands remained up to 20 m above present whereas the first lowstands below present suggest onset of Northern Hemisphere glaciation at 4 Ma. Intensification of global glaciation occurred from 3 Ma to 2.5 Ma, culminating in lowstands similar to the Last Glacial Maximum lowstand at 21,000 years ago and that reoccurred throughout much of the Pleistocene. We attribute the middle Pleistocene transition in ice sheet variability (1.2 Ma to 0.62 Ma) to modulation of 41-thousand-year (kyr) obliquity forcing by an increase in ~100-kyr CO2 variability
Justicia en territorios pesqueros. Violaciones de los derechos humanos de comunidades pesqueras artesanales en el Caribe colombiano
No full textEsta obra analiza la efectividad del sistema jurídico colombiano en la búsqueda de la justicia y la reclamación de derechos humanos en espacios marinos y costeros por medio de las experiencias de tres comunidades pesqueras en Colombia. Una comunidad que no tiene ningún tipo de reconocimiento étnico (Don Jaca), una comunidad indígena wayúu (Manaure) y una comunidad negra (La Boquilla), quienes han reclamado sus derechos sobre sus territorios pesqueros ancestrales por medio del uso de herramientas jurídicas frente a proyectos de infraestructura y desarrollo costero para puertos carboníferos (Sentencia T-229/1993), exploraciones de hidrocarburos off-shore (T-011/2018) y turismo (T-376/2012 y T-226/2016), respectivamente. A través de la revisión de información secundaria y el uso de instrumentos metodológicos participativos, el equipo de investigadoras recopiló el sentir de cada una de las comunidades y logró reconstruir históricamente los cambios y transformaciones sociales y ambientales en el territorio pesquero. Los resultados obtenidos para cada caso de estudio se presentan a partir de la comprensión de los modos de vida y relación de las comunidades con los territorios pesqueros, el conflicto pesquero judicializado (problemáticas y afectaciones), la noción de la justicia en el mar (desde un enfoque de derechos humanos) y las estrategias de defensa y lucha de las comunidades
Plastics from Surface to Seabed: Vertical Distribution of (Micro)plastic Particles in the North Pacific Ocean.
Get PDFIn this study, the vertical distribution of microplastic items across the water column and deep-sea sediments in the North Pacific Ocean, at depths exceeding 5 km, was investigated, covering two previously detected hotspots of surface-floating plastic items, the North Pacific Subtropical Gyre and the World Heritage Site Papaha̅naumokua̅kea Marine National Monument, and a less polluted open ocean site between them. Concentrations ranged from 8 to 2600 items m-3 in the water column and 1100 to 3200 items kg-1 in sediments, with distinct distribution patterns between stations. Our results demonstrate that microplastics are ubiquitously distributed vertically throughout the study sites in the North Pacific Ocean. The similar polymer composition across the samples, dominated by polyethylene and polypropylene, suggests that the plastic items originate from surface fallout, indicating vertical transport as a crucial dispersion pathway. The high abundance of small plastics at the analytical size detection limit of 11 μm is particularly concerning and underscores the necessity to analyze even smaller particles. This study substantially contributes to narrowing critical knowledge gaps regarding distribution and transport pathways of marine plastics in the North Pacific Ocean and provides crucial information for environmental management and policy actions
Differences in acoustic presence and vocal behavior of Spitsbergen’s bowhead whales under ice-covered and open-water conditions
Get PDFArctic-endemic bowhead whales (Balaena mysticetus) are facing extreme habitat changes, particularly due to ongoing sea-ice loss. This study compares acoustic presence and vocal behavior of bowhead whales at two ecologically distinct locations: (1) northwest of Svalbard at 81.5° N, a region that remains nearly ice-covered year-round, and (2) eastern Fram Strait at around 79° N, which is mostly ice-free throughout the year. To detect vocalizations in multi-year acoustic records, two Convolutional Neural Networks were trained. Acoustic presence periods were similar at both locations (October to April), but markedly higher and more continuous acoustic presence northwest of Svalbard indicates increased animal abundance. The frequent detection of song at this site further suggests that it serves as a winter breeding ground. Song diversity peaked in February, possibly reflecting animals arriving from north of Svalbard where sea ice retreated at that time. Regular acoustic detections between 2012 and 2023 in eastern Fram Strait show consistent seasonal presence of bowhead whales in this area. Our study contributes to assessing impacts of ongoing sea-ice decline on the Spitsbergen population and allows for more accurate predictions of future occurrence patterns. We provide new insights into intra-seasonal occurrence, thus support a holistic understanding of ecological characteristics of this population
Reconstructing Eocene Antarctic river drainage from provenance analysis of Amundsen Sea embayment sediments
Get PDFSedimentary records can illuminate relationships between the climate, topography, and glaciation of West Antarctica by revealing its Cenozoic topographic and paleoenvironmental history. Eocene fluvial drainage patterns have previously been inferred using geochemical provenance data from an ~44– to 34–million year deltaic sandstone recovered from the Amundsen Sea Embayment. One interpretation holds that a low-relief, low-lying West Antarctic landscape supported a >1500-kilometer transcontinental river system. Alternatively, higher-relief topography in central West Antarctica formed a drainage divide between the Ross and Amundsen seas. Here, zircon U-Pb data from Amundsen Sea Embayment sediments are examined alongside known regional bedrock provenance signatures. These analyses suggest that all observed provenance indicators in the Eocene sandstone derive from West Antarctic rocks. This implies that a local river system flowed off a West Antarctic drainage divide, helping constrain the mid-Late Eocene evolution of West Antarctic topography with implications for the history of rifting and the characteristics of sediments infilling interior basins
Enhanced CO2 emissions driven by flooding in a simulation of palsa degradation
Get PDFAbstract. Climate change is predicted to put most of the permafrost habitats in the discontinuous zone at risk of disappearing within the next few decades. On a decadal scale, abrupt permafrost thaw may result in larger C losses than gradual permafrost thaw, but drivers of C emissions are poorly understood. To investigate this, we measured C emissions from a palsa under simulated abrupt and gradual thaw scenarios. We continuously measured CO2 and CH4 emissions while deepening the permafrost table under flooded (abrupt) and non-flooded (gradual) conditions. Higher soil-moisture during permafrost thaw is commonly associated with decreasing CO2 and increasing CH4 emissions. Interestingly, our results showed consistent CH4 uptake across all the cores from the palsa and a twofold increase in CO2 emissions under abrupt thaw (flooded conditions). Peat quality analysis (FTIR) showed a higher degradation of C compounds at the permafrost table, likely due to the physical disruption of soil organic matter and the redox changes in the active layer caused by flooding. Averaged CO2 emissions were significantly higher under abrupt thaw (150 mg-CO2 m−2 h−1) compared to gradual thaw (70 mg-CO2 m−2 h−1), with limited permafrost peat contribution. Conversely, permafrost thaw under gradual thaw contributed to a twofold increase in CO2 emissions (57 to 98 mg-CO2 m−3 h−1). Finally, CO2 emissions increased with depth in saturated fens, suggesting that deep-rooted vegetation could be a transport pathway for CO2 outside the growing season. Our findings underline the potential for increased CO2 emissions during the transition to fen conditions under abrupt thaw scenarios and therefore the need for in-situ measurements
Multi-model estimate of Antarctic ice-shelf basal mass budget and ocean drivers
Get PDFAbstract. Societal adaptation to rising sea levels requires robust projections of the Antarctic Ice Sheet's retreat, particularly due to ocean-driven basal melting of its fringing ice shelves. Recent advances in ocean models that simulate ice-shelf melting offer an opportunity to reduce uncertainties in ice–ocean interactions. Here, we compare several community-contributed, circum-Antarctic ocean simulations to highlight inter-model differences, evaluate agreement with satellite-derived melt rates, and examine underlying physical processes. All but one simulation use a melting formulation depending on both thermal driving (T⋆) and friction velocity (u⋆), which together represent the thermal and ocean current forcings at the ice–ocean interface. Simulated melt rates range from 650 to 1277 Gt yr−1 (m=0.45-0.91 m yr−1), driven by variations in model resolution, parameterisations, and sub-ice shelf circulation. Freeze-to-melt ratios span 0.30 % to 30.12 %, indicating large differences in how refreezing is represented. The multi-model mean (MMM), produces an averaged melt rate of 0.64 m yr−1 from a net mass loss of 843 Gt yr−1 (876 Gt yr−1 melting and 33 Gt yr−1 refreezing), yielding a freeze-to-melt ratio of 3.92 %. We define a thermo-kinematic melt sensitivity, ζ=m/(T⋆u⋆)=4.82×10-5 °C−1 for the MMM, with individual models spanning 2.85×10-5 to 19.4×10-5 °C−1. Higher melt rates typically occur near grounding zones where both T⋆ and u⋆ exert roughly equal influence. Because friction velocity is critical for turbulent heat exchange, ice-shelf melting must be characterised by both ocean energetics and thermal forcing. Further work to standardise model setups and evaluation of results against in situ observations and satellite data will be essential for increasing model accuracy, reducing uncertainties, to improve our understanding of ice-shelf–ocean interactions and refine sea-level rise predictions
Environmental conditions modulate hermaphroditic pathways in Salpa thompsoni near the Western Antarctic Peninsula
Get PDFField observations during summer-fall of 2018 in the Antarctic Peninsula region provided the first morphological evidence that under certain environmental conditions, Salpa thompsoni blastozooid development can deviate from its traditional sequential protogynous hermaphroditism (SPH). Early male testis development at female blastozooid stages points to a wide-spread overlapping protogynous hermaphroditism (OPH) in regions where warm Antarctic Circumpolar Current waters mix with colder Antarctic Coastal waters. Our findings highlight the importance of the environmental setting in determining the reproductive pathway in S. thompsoni. OPH was observed in cooler and less productive waters, while SPH occured in both warmer and cooler productive waters. It appears that food availability may offset the effect of decreasing water temperatures for warm-water S. thompsoni reproductive development. It is plausible that OPH may permit the establishment of the S. thompsoni populations in the high Antarctic under the warming trend in the Southern Ocean by allowing for more efficient reproduction