Alfred Wegener Institute for Polar and Marine Research
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Assessing the impact of Ocean Alkalinity Enhancement on the zooplankton community
Get PDFOcean alkalinity enhancement (OAE) can help mitigate climate change impacts by increasing the carbon storage capacity of the ocean. The technique involves addition of alkaline substances to the seawater to accelerate the natural rock weathering process. However, this will lead to sudden seawater chemistry changes, such as increased pH that might directly and/or indirectly (through trophic pathways) affect zooplankton, an important trophic link, by altering its metabolic state and community composition. In addition, varying dilution times of alkaline substances might impact organisms differently. To date, the possible influences of OAE on zooplankton communities are largely unexplored. To bridge the knowledge gap, we conducted mesocosm and laboratory experiments in simulated non-equilibrated, calcium-based (Ca(OH)2) OAE setups. An incrementally enhanced alkalinity gradient from 0 to 1250 &#181;mol kg-1 in steps of 250 &#181;mol kg-1 was used in all experiments. The wide-ranging enhanced total alkalinity (&#8710;TA) was selected to assess the safety threshold. In addition, we compared immediate versus delayed dilution scenarios in our mesocosm study, where each scenario ended up with the same &#8710;TA gradient after mixing. We examined the multitrophic community response by monitoring twelve mesocosms for 39 days including the natural spring bloom community of Helgoland roads waters in the North Sea. Subsequently, the direct effect of alkalinity enhancement on the physiology (i.e., respiration and grazing) of Temora longicornis (predominant copepod in the mesocosms) was evaluated in the laboratory. The species-specific bottom-up effect was examined by culturing Rhodomonas salina in aforementioned &#8710;TA gradient and feeding them to the T. longicornis. We observed relatively lower zooplankton abundance, and growth rate in mesocosms with &#8710;TA1000 and 1250 &#181;mol kg-1, which might be a bottom-up effect. In our lab experiments, though, we observed a negative impact on R. salina growth rate and nutritional quality from &#8710;TA750 &#181;mol kg-1, we did not detect any substantial direct or indirect impact on the physiological performance of T. longicornis. Overall, our laboratory study provided a preliminary understanding of the direct and indirect effects of OAE on a key copepod species, and the mesocosm study gave insight into the zooplankton community response.</jats:p
Abrupt excursions in water vapor isotopic variability at the Pointe Benedicte observatory on Amsterdam Island
Get PDFIn order to complement the picture of the atmospheric water cycle in the Southern Ocean, we have continuously monitored water vapor isotopes since January 2020 on Amsterdam Island in the Indian Ocean. We present here the first 2-year long water vapor isotopic record at this site. We show that the water vapor isotopic composition largely follows the water vapor mixing ratio, as expected in marine boundary layers. However, we detect 11 periods of a few days where there is a strong loss of correlation between water vapor δ18O and water vapor mixing ratio as well as abrupt negative excursions of water vapor δ18O. These excursions often occur toward the end of precipitation events. Six of these events show a decrease in gaseous elemental mercury, suggesting subsidence of air from a higher altitude. Our study aims to further explore the mechanism driving these negative excursions in water vapor δ18O. We used two different models to provide a data–model comparison over this 2-year period. While the European Centre Hamburg model (ECHAM6-wiso) at 0.9° was able to reproduce most of the sharp negative water vapor δ18O excursions, hence validating the physics process and isotopic implementation in this model, the Laboratoire de Météorologie Dynamique Zoom model (LMDZ-iso) at 2° (3°) resolution was only able to reproduce seven (one) of the negative excursions, highlighting the possible influence of the model resolution for the study of such abrupt isotopic events. Based on our detailed model–data comparison, we conclude that the most plausible explanations for such isotopic excursions are rain–vapor interactions associated with subsidence at the rear of a precipitation event
On the length and intensity of the West African summer monsoon during the last interglacial African humid period
Get PDFThe increase in summer monsoon precipitation over western Africa during the last interglacial (LIG) relative to
the pre-industrial (PI) is well documented, but it is uncertain whether this increase is due to larger rainfall rate
alone, an extension of the summer monsoon season or a combination of the two. Due to different orbital config-
uration, the boreal summer of the LIG was warmer but shorter than the PI, potentially influencing the summer
monsoon duration. In this study, we employ a newly developed isotope-enabled climate model, AWI-ESM-wiso
to investigate the intensity and length of the West African Summer Monsoon (WASM) for both LIG and PI time
periods. Our model results indicate that, despite an intensification in summer insolation and an enhanced hydro-logical cycle, WASM season in the LIG is 9 days shorter compared to the PI. During the LIG, increased insolation in late spring and early summer strengthens the Saharan heat low (SHL) and its associated sub-systems, facilitating a faster accumulation of potential instability and an earlier WASM onset. However, a substantial earlier
withdrawal of the WASM is also detected, driven by an earlier southward shift of insolation maximum. More-
over, our findings are further supported by models participating in the 4th phase of the Paleoclimate Modelling
Intercomparison Project (PMIP4)
Glacial isostatic adjustment reduces past and future Arctic subsea permafrost
Get PDFSea-level rise submerges terrestrial permafrost in the Arctic, turning it into subsea permafrost. Subsea permafrost underlies ~ 1.8 million km2 of Arctic continental shelf, with thicknesses in places exceeding 700 m. Sea-level variations over glacial-interglacial cycles control subsea permafrost distribution and thickness, yet no permafrost model has accounted for glacial isostatic adjustment (GIA), which deviates local sea level from the global mean due to changes in ice and ocean loading. Here we incorporate GIA into a pan-Arctic model of subsea permafrost over the last 400,000 years. Including GIA significantly reduces present-day subsea permafrost thickness, chiefly because of hydro-isostatic effects as well as deformation related to Northern Hemisphere ice sheets. Additionally, we extend the simulation 1000 years into the future for emissions scenarios outlined in the Intergovernmental Panel on Climate Change’s sixth assessment report. We find that subsea permafrost is preserved under a low emissions scenario but mostly disappears under a high emissions scenario
Gold Mining as key to Eastern Beringia - Impressions from the AWI Expedition 2023 to the Klondike Goldfields
Get PDFIn the summer of 2023, three colleagues from the AWI Research Unit Potsdam worked together with two Canadian colleagues from the University of Toronto on permafrost outcrops in the vicinity of Dawson City. Dawson City is located in western Canada in the Yukon Territory near the Alaskan border at the mouth of the Klondike River into the Yukon and is known for its gold mining.
During the Klondike Gold Rush at the end of the 19th century, tens of thousands of gold miners had spent several years in the Klondike Goldfields digging shafts in the permafrost with fires during the winter, driving tunnels horizontally and bringing the gold-bearing gravels to the surface. In the early 20th century through the 1960s, gold was washed out on a large scale in the main valleys with huge dredges, massively altering the landscape. Today, dozens of smaller and larger gold mines extract the gold placers and further alter the landscape. Huge sand and gravel mountains and long gravel walls with little vegetation cover can still be found on the valley floors today.
The very continental climate in the study area leads to very cold winters (up to -50°C) and very warm summers. With temperatures up to 30°C and a very low mosquito density, we were able to sample the permafrost partly in T-shirts. Another consequence of the dry heat with only a few thundershowers were over 100 forest fires in the region, which, in addition to frequent smoke in Dawson City and the surrounding area, also led to evacuations of towns in the wider area and road closures.
In the secondary valleys, the ice-rich permafrost overlying gold-bearing gravels is still being thawed with water cannons and removed with excavators. This created short-term opportunities for us to examine fresh permafrost walls. Our group examined and sampled both the long and wide ice wedges and the surrounding ice-rich sediment. Studies of ice chemistry and ice isotopy are planned. Different age determination methods will be carried out on the sediments and the ice. The sediments will be analyzed for grain size, carbon and nitrogen contents, and biomarkers, among other things, and will be available for paleoecological studies to reconstruct environmental conditions before, during, and after the last ice age.
We would like to give you an impression of this expedition with some pictures and background information
A Synthesis of Global Coastal Ocean Greenhouse Gas Fluxes
Get PDFThe coastal ocean contributes to regulating atmospheric greenhouse gas concentrations by taking up carbon dioxide (CO2) and releasing nitrous oxide (N2O) and methane (CH4). In this second phase of the Regional Carbon Cycle Assessment and Processes (RECCAP2), we quantify global coastal ocean fluxes of CO2, N2O and CH4 using an ensemble of global gap-filled observation-based products and ocean biogeochemical models. The global coastal ocean is a net sink of CO2 in both observational products and models, but the magnitude of the median net global coastal uptake is ∼60% larger in models (−0.72 vs. −0.44 PgC year−1, 1998–2018, coastal ocean extending to 300 km offshore or 1,000 m isobath with area of 77 million km2). We attribute most of this model-product difference to the seasonality in sea surface CO2 partial pressure at mid- and high-latitudes, where models simulate stronger winter CO2 uptake. The coastal ocean CO2 sink has increased in the past decades but the available time-resolving observation-based products and models show large discrepancies in the magnitude of this increase. The global coastal ocean is a major source of N2O (+0.70 PgCO2-e year−1 in observational product and +0.54 PgCO2-e year−1 in model median) and CH4 (+0.21 PgCO2-e year−1 in observational product), which offsets a substantial proportion of the coastal CO2 uptake in the net radiative balance (30%–60% in CO2-equivalents), highlighting the importance of considering the three greenhouse gases when examining the influence of the coastal ocean on climate
Justice in fishing territories: Human rights violations in artisanal fisheries analyzed by the Colombian Constitutional Court
Get PDFSeas and inland waters have historically been spaces where social struggles have been overlooked and made invisible. This article offers an interdisciplinary analysis of the Colombian Constitutional Court decisions related to human rights violations in artisanal fishing territories. We used a human rights-based approach to study 79 Constitutional Injunctions (Acciones de Tutela) and built a digital database 'Justice in Fishing Territories' (Justicia en Territorios Pesqueros). We identify and discuss the most frequently claimed and protected rights. Most Court proceedings are centered on participatory processes, indicating that actors within the artisanal fisheries sector are excluded from the discussion and approval of development projects. We conclude that the Colombian State has historically privileged the interests of industrial economic sectors to the detriment of the ways of living, territories, and rights of artisanal fishing populations.</jats:p
Decadal-scale variability and warming affect spring timing and forest growth across the western Great Lakes region
Get PDFThe Great Lakes region of North America has warmed by 1–2 °C on average since pre-industrial times, with the most pronounced changes observable during winter and spring. Interannual variability in temperatures remains high, however, due to the influence of ocean-atmosphere circulation patterns that modulate the warming trend across years. Variations in spring temperatures determine growing season length and plant phenology, with implications for whole ecosystem function. Studying how both internal climate variability and the “secular” warming trend interact to produce trends in temperature is necessary to estimate potential ecological responses to future warming scenarios. This study examines how external anthropogenic forcing and decadal-scale variability influence spring temperatures across the western Great Lakes region and estimates the sensitivity of regional forests to temperature using long-term growth records from tree-rings and satellite data. Using a modeling approach designed to test for regime shifts in dynamic time series, this work shows that mid-continent spring climatology was strongly influenced by the 1976/1977 phase change in North Pacific atmospheric circulation, and that regional forests show a strengthening response to spring temperatures during the last half-century