Petra Zahajská

Primary production in the northeastern Arabian Sea is a key component of regional biogeochemical cycling and oxygen minimum zone development, linking monsoon circulation to nutrient cycling and carbon export. Today, primary production is influenced by both components of the South Asian monsoon system, with the South Asian summer monsoon (SASM) affecting coastal nutrient supply, whereas winter monsoon (SAWM) winds promote surface cooling and convective mixing. However, how the relative influence of these monsoonal systems changes under different climatic and oceanographic boundary conditions remains poorly understood. By combining plant-wax stable carbon and hydrogen isotopes, alkenone-derived sea surface temperature (SST), hyperspectral imaging of chloropigments- a , and alkenone concentration from the sediment core SO130-289KL, we reconstruct hydroclimate, SST, and marine primary production between 23,000 and 2,000 years before 2000 (b2k). Our reconstruction indicates progressive strengthening of SASM precipitation from the Last Glacial Maximum into the Holocene, interrupted by pronounced aridity during Heinrich Stadial 1 and Greenland Stadial 1. SST broadly followed deglacial warming in the Northern Hemisphere but showed substantial regional variability associated with SAWM strength. We further identify two intervals of increased winter precipitation between 14,000–10,500 and 4,000–2,000 years b2k. Primary production shows no clear correspondence with either monsoon system alone. During glacial conditions, lower sea level placed the core site closer to the productive coastal zone, increasing its sensitivity to changes in SASM strength. During the Early Holocene increased oxygenation of intermediate waters suppressed low-oxygen nutrient recycling, where after ~6,000 years b2k weaker ventilation promoted higher production despite weaker monsoons.

Worldwide, lacustrine ecosystems are threatened by eutrophication and deoxygenation. Both processes are driven by the combined effects of human activities and climate change. Understanding the pre‐anthropogenic nexus between warming, eutrophication, deoxygenation, and related feedback is essential to determine how lakes respond to rapid climate change. We investigate the responses of primary producers, stratification, and nutrient cycling in a small Central European lake (Übeschisee, Swiss Plateau) to rapid climate change during Late Glacial times (17–11 ka). After 16.2 ka (Heinrich Stadial; HS1) and during the Bølling/Allerød interstadial, Übeschisee experienced natural eutrophication following summer warming and vegetation development in the catchment. Anoxia events with blooms of sulfur bacteria systematically established during colder periods of HS1 (16.5 ka), the Older Dryas (14 ka), the Gerzensee Oscillation (13.2 ka), and the Younger Dryas (12.7–11.7 ka). Anoxia events also caused reductive dissolution of Mn; labile P was always efficiently recycled. Algal communities responded to anoxia events, but the excursions of community composition were reversible. Ti follows NGRIP Dust, suggesting that Übeschisee provides a continuous record of dust deposition with high rates during colder periods. The paired lake approach with adjacent Amsoldingersee shows that the results are robust and regionally reproducible, and that common drivers influenced both lakes simultaneously.

Predicting the trajectory of aquatic deoxygenation under global warming requires a mechanistic understanding of lacustrine responses to rapid climate shifts. We investigated how climate-driven changes in catchment vegetation and local iron-rich lithology regulated lake stratification and ecosystem resilience in the maar lake Holzmaar (Central Europe). We focused on the Late Glacial, specifically on transitions during Dansgaard-Oeschger Event 1 (DOE-1; ca. 14 690–11 700 cal yr BP), a period of rapid natural warming and cooling that serves as an analogue for future high amplitude climate variation and for modern Arctic lakes undergoing rapid climate-driven transitions. Combining non-destructive hyperspectral imaging (HSI) of sedimentary pigments with high-resolution XRF geochemistry, we resolved parts of the ecosystem trajectory during DOE-1. The primary producer community shifted from an oligotrophic cyanobacterial and low-light Pleniglacial assemblage to a stable, stratified Allerød assemblage, characterized by the planktonic diatom Stephanodiscus minutulus and anoxygenic purple sulphur bacteria (PSB) in the photic zone. While regional warming (mean summer temperature increased ∼ 2.8 °C) provided the physical potential for lake stratification, our data suggest that intense anoxia was primarily triggered by the expansion of Betula in the watershed. This afforestation stabilized the water column through wind shielding. The termination of the anoxic phase coincided with the onset of the Younger Dryas cooling and increased aridity, which effectively destabilized the existing stratification. While the shift from Betula to Pinus forest may have caused a change in the terrestrial-aquatic linkage, the primary driver of the transition was the physical forcing (lake mixing) of the climatic shift (cooling). Geochemically, the lake exhibited remarkable resilience. Unlike carbonate-dominated systems prone to internal phosphorus loading, Holzmaar efficiently sequesters nutrients via a dual mechanism of reactive iron binding (authigenic vivianite) and stable mineral burial. The phosphorus trap prevents nutrient release by permanently sequestering P in the sediment, allowing rapid ecosystem recovery without delay once the specific climate and vegetation drivers shift. Our findings demonstrate that in volcanic maar lakes, catchment vegetation characteristics and local lithology can modulate, and even override, the direct effects of climate warming on aquatic anoxia.

Reconstructing past South Asian monsoon dynamics, which governs wind and rainfall patterns across the Indian subcontinent, is crucial for understanding low-latitude climate. Constraining monsoon drivers requires separating summer and winter components in palaeoclimate archives, but this remains challenging because proxy signals usually integrate seasonal signals. The northeastern Arabian Sea provides a unique setting in which sedimentary and geochemical proxies are driven by the summer monsoon, while sea surface temperature is primarily controlled by winter monsoon winds. Here we employed mass spectrometry and hyperspectral imaging on a sediment core off Pakistan to reconstruct subdecadal changes in sea surface temperature and marine primary production during the last deglaciation (~16,000–12,000 years ago). Atmospheric humidity and vegetation changes were additionally assessed by plant-wax isotope analyses on a subset of samples. We show that summer monsoon winds were driven by the Northern Hemisphere high-latitude climate on centennial-to-millennial timescales. Winter monsoon was primarily characterized by a millennial-scale decline in wind strength driven by increasing global temperatures, with superimposed centennial-scale variability. We identified an inverse relationship between winter monsoon wind strength and the amount of winter non-monsoonal precipitation. Mechanistic insights of seasonal monsoon dynamics improved interpretation of regional palaeoprecipitation records and may enhance climate model performances in low latitudes.

Predicting the trajectory of aquatic deoxygenation under global warming requires a mechanistic understanding of lacustrine responses to rapid climate shifts. We investigated how climate-driven changes in catchment vegetation and local iron-rich lithology regulated lake stratification and ecosystem resilience in the maar lake Holzmaar (Central Europe). We focused on the Late Glacial, specifically on transitions during Dansgaard-Oeschger Event 1 (DOE-1; ca. 14,690–11,700 cal yr BP), a period of rapid natural warming and cooling that serves as an analogue for future high amplitude climate variation and for modern Arctic lakes undergoing rapid climate-driven transitions. Combining non-destructive hyperspectral imaging (HSI) of sedimentary pigments with high-resolution XRF geochemistry, we resolved parts of the ecosystem trajectory during DOE-1. Ecological succession progress from a pioneer community of cyanobacteria to a stable anoxic late-successional community characterized by planktonic diatom Stephanodiscus minutulus and anoxygenic purple sulphur bacteria (PSB) in the photic zone. While regional warming (mean summer temperature increased ~2.8 °C) provided the physical potential for lake stratification, our data suggest that intense anoxia was primarily triggered by the expansion of Betula in the watershed. This afforestation stabilized the water column through wind shielding. The termination of the anoxic phase coincided with the onset of the Younger Dryas cooling and increased aridity, which effectively destabilized the existing stratification. While the shift from Betula to Pinus forest may have caused a change in the terrestrial-aquatic linkage, the primary driver of the transition was the physical forcing (lake mixing) of the climatic shift (cooling). Geochemically, the lake exhibited remarkable resilience. Unlike carbonate-dominated systems prone to internal phosphorus loading, Holzmaar efficiently sequesters nutrients via a dual mechanism of reactive iron binding (authigenic vivianite) and stable mineral burial. The phosphorous trap prevents nutrient release by permanently sequestering P in the sediment, allowing rapid ecosystem recovery without delay once the specific climate and vegetation drivers shift. Our findings demonstrate that in volcanic maar lakes, catchment vegetation characteristics and local lithology can modulate, and even override, the direct effects of climate warming on aquatic anoxia.

Predicting the trajectory of aquatic deoxygenation under global warming requires a mechanistic understanding of lacustrine responses to rapid climate shifts. We investigated how climate-driven changes in catchment vegetation and local iron-rich lithology regulated lake stratification and ecosystem resilience in the maar lake Holzmaar (Central Europe). We focused on the Late Glacial, specifically on transitions during Dansgaard-Oeschger Event 1 (DOE-1; ca. 14,690–11,700 cal yr BP), a period of rapid natural warming and cooling that serves as an analogue for future high amplitude climate variation and for modern Arctic lakes undergoing rapid climate-driven transitions. Combining non-destructive hyperspectral imaging (HSI) of sedimentary pigments with high-resolution XRF geochemistry, we resolved parts of the ecosystem trajectory during DOE-1. Ecological succession progress from a pioneer community of cyanobacteria to a stable anoxic late-successional community characterized by planktonic diatom Stephanodiscus minutulus and anoxygenic purple sulphur bacteria (PSB) in the photic zone. While regional warming (mean summer temperature increased ~2.8 °C) provided the physical potential for lake stratification, our data suggest that intense anoxia was primarily triggered by the expansion of Betula in the watershed. This afforestation stabilized the water column through wind shielding. The termination of the anoxic phase coincided with the onset of the Younger Dryas cooling and increased aridity, which effectively destabilized the existing stratification. While the shift from Betula to Pinus forest may have caused a change in the terrestrial-aquatic linkage, the primary driver of the transition was the physical forcing (lake mixing) of the climatic shift (cooling). Geochemically, the lake exhibited remarkable resilience. Unlike carbonate-dominated systems prone to internal phosphorus loading, Holzmaar efficiently sequesters nutrients via a dual mechanism of reactive iron binding (authigenic vivianite) and stable mineral burial. The phosphorous trap prevents nutrient release by permanently sequestering P in the sediment, allowing rapid ecosystem recovery without delay once the specific climate and vegetation drivers shift. Our findings demonstrate that in volcanic maar lakes, catchment vegetation characteristics and local lithology can modulate, and even override, the direct effects of climate warming on aquatic anoxia.

Predicting the trajectory of aquatic deoxygenation under global warming requires a mechanistic understanding of lacustrine responses to rapid climate shifts. We investigated how climate-driven changes in catchment vegetation and local iron-rich lithology regulated lake stratification and ecosystem resilience in the maar lake Holzmaar (Central Europe). We focused on the Late Glacial, specifically on transitions during Dansgaard-Oeschger Event 1 (DOE-1; ca. 14,690–11,700 cal yr BP), a period of rapid natural warming and cooling that serves as an analogue for future high amplitude climate variation and for modern Arctic lakes undergoing rapid climate-driven transitions. Combining non-destructive hyperspectral imaging (HSI) of sedimentary pigments with high-resolution XRF geochemistry, we resolved parts of the ecosystem trajectory during DOE-1. Ecological succession progress from a pioneer community of cyanobacteria to a stable anoxic late-successional community characterized by planktonic diatom Stephanodiscus minutulus and anoxygenic purple sulphur bacteria (PSB) in the photic zone. While regional warming (mean summer temperature increased ~2.8 °C) provided the physical potential for lake stratification, our data suggest that intense anoxia was primarily triggered by the expansion of Betula in the watershed. This afforestation stabilized the water column through wind shielding. The termination of the anoxic phase coincided with the onset of the Younger Dryas cooling and increased aridity, which effectively destabilized the existing stratification. While the shift from Betula to Pinus forest may have caused a change in the terrestrial-aquatic linkage, the primary driver of the transition was the physical forcing (lake mixing) of the climatic shift (cooling). Geochemically, the lake exhibited remarkable resilience. Unlike carbonate-dominated systems prone to internal phosphorus loading, Holzmaar efficiently sequesters nutrients via a dual mechanism of reactive iron binding (authigenic vivianite) and stable mineral burial. The phosphorous trap prevents nutrient release by permanently sequestering P in the sediment, allowing rapid ecosystem recovery without delay once the specific climate and vegetation drivers shift. Our findings demonstrate that in volcanic maar lakes, catchment vegetation characteristics and local lithology can modulate, and even override, the direct effects of climate warming on aquatic anoxia.

Predicting the trajectory of aquatic deoxygenation under global warming requires a mechanistic understanding of lacustrine responses to rapid climate shifts. We investigated how climate-driven changes in catchment vegetation and local iron-rich lithology regulated lake stratification and ecosystem resilience in the maar lake Holzmaar (Central Europe). We focused on the Late Glacial, specifically on transitions during Dansgaard-Oeschger Event 1 (DOE-1; ca. 14,690–11,700 cal yr BP), a period of rapid natural warming and cooling that serves as an analogue for future high amplitude climate variation and for modern Arctic lakes undergoing rapid climate-driven transitions. Combining non-destructive hyperspectral imaging (HSI) of sedimentary pigments with high-resolution XRF geochemistry, we resolved parts of the ecosystem trajectory during DOE-1. Ecological succession progress from a pioneer community of cyanobacteria to a stable anoxic late-successional community characterized by planktonic diatom Stephanodiscus minutulus and anoxygenic purple sulphur bacteria (PSB) in the photic zone. While regional warming (mean summer temperature increased ~2.8 °C) provided the physical potential for lake stratification, our data suggest that intense anoxia was primarily triggered by the expansion of Betula in the watershed. This afforestation stabilized the water column through wind shielding. The termination of the anoxic phase coincided with the onset of the Younger Dryas cooling and increased aridity, which effectively destabilized the existing stratification. While the shift from Betula to Pinus forest may have caused a change in the terrestrial-aquatic linkage, the primary driver of the transition was the physical forcing (lake mixing) of the climatic shift (cooling). Geochemically, the lake exhibited remarkable resilience. Unlike carbonate-dominated systems prone to internal phosphorus loading, Holzmaar efficiently sequesters nutrients via a dual mechanism of reactive iron binding (authigenic vivianite) and stable mineral burial. The phosphorous trap prevents nutrient release by permanently sequestering P in the sediment, allowing rapid ecosystem recovery without delay once the specific climate and vegetation drivers shift. Our findings demonstrate that in volcanic maar lakes, catchment vegetation characteristics and local lithology can modulate, and even override, the direct effects of climate warming on aquatic anoxia.

Predicting the trajectory of aquatic deoxygenation under global warming requires a mechanistic understanding of lacustrine responses to rapid climate shifts. We investigated how climate-driven changes in catchment vegetation and local iron-rich lithology regulated lake stratification and ecosystem resilience in the maar lake Holzmaar (Central Europe). We focused on the Late Glacial, specifically on transitions during Dansgaard-Oeschger Event 1 (DOE-1; ca. 14,690–11,700 cal yr BP), a period of rapid natural warming and cooling that serves as an analogue for future high amplitude climate variation and for modern Arctic lakes undergoing rapid climate-driven transitions. Combining non-destructive hyperspectral imaging (HSI) of sedimentary pigments with high-resolution XRF geochemistry, we resolved parts of the ecosystem trajectory during DOE-1. Ecological succession progress from a pioneer community of cyanobacteria to a stable anoxic late-successional community characterized by planktonic diatom Stephanodiscus minutulus and anoxygenic purple sulphur bacteria (PSB) in the photic zone. While regional warming (mean summer temperature increased ~2.8 °C) provided the physical potential for lake stratification, our data suggest that intense anoxia was primarily triggered by the expansion of Betula in the watershed. This afforestation stabilized the water column through wind shielding. The termination of the anoxic phase coincided with the onset of the Younger Dryas cooling and increased aridity, which effectively destabilized the existing stratification. While the shift from Betula to Pinus forest may have caused a change in the terrestrial-aquatic linkage, the primary driver of the transition was the physical forcing (lake mixing) of the climatic shift (cooling). Geochemically, the lake exhibited remarkable resilience. Unlike carbonate-dominated systems prone to internal phosphorus loading, Holzmaar efficiently sequesters nutrients via a dual mechanism of reactive iron binding (authigenic vivianite) and stable mineral burial. The phosphorous trap prevents nutrient release by permanently sequestering P in the sediment, allowing rapid ecosystem recovery without delay once the specific climate and vegetation drivers shift. Our findings demonstrate that in volcanic maar lakes, catchment vegetation characteristics and local lithology can modulate, and even override, the direct effects of climate warming on aquatic anoxia.

Predicting the trajectory of aquatic deoxygenation under global warming requires a mechanistic understanding of lacustrine responses to rapid climate shifts. We investigated how climate-driven changes in catchment vegetation and local iron-rich lithology regulated lake stratification and ecosystem resilience in the maar lake Holzmaar (Central Europe). We focused on the Late Glacial, specifically on transitions during Dansgaard-Oeschger Event 1 (DOE-1; ca. 14,690–11,700 cal yr BP), a period of rapid natural warming and cooling that serves as an analogue for future high amplitude climate variation and for modern Arctic lakes undergoing rapid climate-driven transitions. Combining non-destructive hyperspectral imaging (HSI) of sedimentary pigments with high-resolution XRF geochemistry, we resolved parts of the ecosystem trajectory during DOE-1. Ecological succession progress from a pioneer community of cyanobacteria to a stable anoxic late-successional community characterized by planktonic diatom Stephanodiscus minutulus and anoxygenic purple sulphur bacteria (PSB) in the photic zone. While regional warming (mean summer temperature increased ~2.8 °C) provided the physical potential for lake stratification, our data suggest that intense anoxia was primarily triggered by the expansion of Betula in the watershed. This afforestation stabilized the water column through wind shielding. The termination of the anoxic phase coincided with the onset of the Younger Dryas cooling and increased aridity, which effectively destabilized the existing stratification. While the shift from Betula to Pinus forest may have caused a change in the terrestrial-aquatic linkage, the primary driver of the transition was the physical forcing (lake mixing) of the climatic shift (cooling). Geochemically, the lake exhibited remarkable resilience. Unlike carbonate-dominated systems prone to internal phosphorus loading, Holzmaar efficiently sequesters nutrients via a dual mechanism of reactive iron binding (authigenic vivianite) and stable mineral burial. The phosphorous trap prevents nutrient release by permanently sequestering P in the sediment, allowing rapid ecosystem recovery without delay once the specific climate and vegetation drivers shift. Our findings demonstrate that in volcanic maar lakes, catchment vegetation characteristics and local lithology can modulate, and even override, the direct effects of climate warming on aquatic anoxia.