Limnology and Oceanography最新文献

From spring 2022 to late summer 2024, a study of Lake Ilay's water column and sediment cores analyzed key environmental parameters. Conductivity, temperature, and chlorophyll-a were measured at 2 m, while pH, conductivity, temperature, calcium (Ca²⁺), and alkalinity were monitored within the top 20 m. The lake exhibited significant seasonal variations, remaining thermally and chemically stratified for at least 8 months yearly. Six sediment cores (1–23 m depth) were analyzed for mineralogy, dry bulk density, and organic/inorganic carbon, complemented by cryo-scanning electron microscopy observations. This multi-analytical approach provided insights into micrite precipitation, the primary component of lacustrine carbonate muds. Building on these findings, an integrated model for carbonate production in stratified lakes was developed. It incorporates ionic circulation between the water column and sediment, offering a novel framework for micrite formation. This approach carries broad implications for lacustrine and marine systems over geological timescales, shedding light on carbonate precipitation processes, ion dynamics, and their availability across the fluid envelope and the sedimentary reservoir. A key finding is that carbonate production in the water column is brief in time, with preservation and accumulation restricted to shoreline platforms, submerged under shallow water, that form a belt around the lake. However, lacustrine micrite formation continues in sediments at all depths, linked to exopolymer degradation. The carbonate platforms result from vertical accretion, and their lateral extent is defined by the lower boundary of carbonate dissolution along the topographic slope.

We investigated the occurrence pattern of Salpa fusiformis, broad-spectrum filter-feeding zooplankton that intercept small particles around the Kuroshio Current, off southern Japan and inferred in situ distribution of near-surface small microplastics (plastic particles < 330 μm) based on their gut contents. First, we examined 98 neuston net samples to determine the distribution of S. fusiformis. While no S. fusiformis were found in the daytime samples, they occurred in 75% of the night samples, indicating active diel vertical migration. Their nocturnal density in the surface layer was 0.026–0.82 ind. m⁻³ and was particularly high around the cold-core ring within the large meander of the Kuroshio Current. Microplastics were found in 98% of the guts of S. fusiformis (mean: 5.23 ± 4.40 particles/ind.). The in situ density of near-surface small microplastics estimated from their gut content analysis ranged from 194 ± 138 to 7093 ± 923 particles m⁻³. The estimated small microplastics density was negatively correlated with surface current velocity, while small microplastic size and polymer compositions were spatially variable. This suggests that the small microplastic distribution was influenced by oceanographic conditions and location of pollution sources. The maximum small microplastic ingestion rate by S. fusiformis in the surface layer (< 0.75 m depth) was 34.5 particles m⁻³ d⁻¹, corresponding to 1.05% of the in situ small microplastic density. Overall, the uptake efficiency of small microplastics from the water column may be substantial owing to the active diel vertical migration and production of large fecal pellets by S. fusiformis.

In the Southern Ocean, phytoplankton are critical drivers of biogeochemical cycling and food web dynamics, and show sensitivity to shifting climates. Along the West Antarctic Peninsula, climate-driven variations in sea ice and hydrography have been linked to long-term changes in summer phytoplankton productivity. Such changes are hypothesized to reflect decadal shifts in algal light environments, but diagnostic evidence of this light-dependent response is limited. Using a 27-yr timeseries of summer phytoplankton pigments and productivity collected along the West Antarctic Peninsula by the Palmer Long Term Ecological Research (LTER) program, we quantified trends in surface phytoplankton photophysiology, productivity, and composition in response to environmental change. Our results revealed a decadal doubling in proportions of phytoplankton photoprotective pigments correlated with long-term shoaling and strengthening of mixed layer depths. This biophysical signature is consistent with photophysiological response to increased light supply, signifying a long-term shift in light environments for surface phytoplankton. The long-term change in community pigment signature could not be explained by trends in phytoplankton composition alone, indicating a key role of photoacclimation. Phytoplankton community biomass, productivity, and production efficiency (chlorophyll-normalized productivity) were similarly correlated to upper ocean structure and increased decadally, demonstrating a functional benefit from enhanced light availability. These physiological findings support the hypothesis that decadal trends in summer production along the peninsula are light-dependent. Such large-scale shifts in community pigment signature, linked to oceanographic forcing, suggest that photophysiological indices provide useful insights into how shifting climates will influence phytoplankton communities.