Limnology and Oceanography Letters最新文献

Understanding the fate of permafrost-derived dissolved organic matter (DOM) is critical for unraveling its role in carbon cycling. However, it remains unclear whether the high lability of permafrost-derived DOM can be attributed to intrinsic chemical properties or elevated carbon concentrations. We investigated the dynamics of permafrost DOM from the Qinghai–Tibetan Plateau using both biodegradation and photodegradation experiments. Biodegradation and photodegradation of permafrost-derived DOM exhibited distinct qualitative preferences for specific chemical groups (i.e., peptide-like and aromatics, respectively). Notably, reducing the initial concentration of dissolved organic carbon (DOC) by half and a quarter resulted in shifts in biodegradable DOC content from 11.2% to 11.5% and 8.5%, respectively, accompanied by a corresponding decrease in the biodegradation rate from 0.11 to 0.06 and 0.03. This insight highlights the importance of recognizing the interplay between DOM quality and concentration and bears broader significance for our understanding of the fate of permafrost-derived DOM in natural ecosystems.

Water temperature responses to climate change may vary across Earth's estuaries. To understand how climate change influences estuarine surface water temperature, we need global, long-term records of estuarine temperature. Here, we generated surface water temperature data over 1060 estuaries globally using Landsat 5, 7, and 8 from 1985 to 2022 and compared water warming rates with local air temperature warming rates. Forty-seven percent of Earth's estuaries are warming, with a global average warming rate of 0.070 ± 0.004°C yr⁻¹ (median = 0.060°C yr⁻¹). Estuaries at higher latitudes showed rapid warming. A 1°C increase in air temperature could lead to a 0.81°C increase in estuarine surface water warming and 1.3°C increase in estuaries above 60.5°N. We inferred the potential influences over estuarine warming based on distinct global spatial patterns in water and air warming and discussed the effects of warming water temperature on estuarine metabolism and water quality.

Understanding species phenology and temporal co-occurrence across trophic levels is essential to assess anthropogenic impacts on ecological interactions. We analyzed 15 yr of monitoring data to identify trends and drivers of timing and magnitude of bloom-forming phytoplankton and diverse zooplankton taxa in the central Baltic Sea. We show that the timings of phytoplankton blooms advance, whereas crustacean zooplankton seasonal timings remain constant. This increasing offset with the spring bloom is linked to the decline of Pseudocalanus, a key copepod sustaining pelagic fish production. The majority of copepod and cladoceran taxa, however, are co-occurring with summer blooms. We also find new developing fall blooms, fueling secondary production later in the season. Our study highlights that response to climate change differs within and between functional groups, stressing the importance of investigating plankton phenologies over the entire annual cycle in pelagic systems.

Although trends toward earlier ice-out have been documented globally, the links between ice-out timing and lake thermal and biogeochemical structure vary spatially. In high-latitude lakes where ice-out occurs close to peak intensity of solar radiation, these links remain unclear. Using a long-term dataset from 13 lakes in West Greenland, we investigated how changing ice-out and weather conditions affect lake thermal structure and oxygen concentrations. In early ice-out years, lakes reach higher temperatures across the water column and have deeper epilimnia. Summer hypolimnia are the warmest (~ 11°C) in years when cooler air temperatures follow early ice-out, allowing full lake turnover. Due to the higher potential for substantive spring mixing in early ice-out years, a warmer hypolimnion is associated with higher dissolved oxygen concentrations. By affecting variability in spring mixing, the consequences of shifts in ice phenology for lakes at high latitudes differ from expectations based on temperate regions.

Libraries of inherent optical properties (IOPs) of microplastics are sparse, yet they are essential for the development of optical techniques to detect and quantify microplastics in the ocean. In this study, we describe our results and technique for the measurement of the IOPs of microplastic suspensions generated from commonly utilized plastics. The measurements included angle-resolved polarized light scattering, and spectral absorption and beam attenuation coefficients. We also performed ancillary characterization of particle properties, including size distribution, shape, and mass concentration of suspended matter. We observed several unique optical characteristics regarding absorption, scattering, and polarization properties compared with typical marine particle assemblages. We show that these results are useful for radiative transfer simulations as well as the potential development of novel plastic detection techniques from above- or in-water optical measurements.

The storage of organic carbon in the soils of salt marshes and other coastal blue carbon ecosystems has gained considerable attention by the scientific community for more than a decade now, while the relevance and mechanisms of soil inorganic carbon accumulation remain poorly understood. Using long-term annual accretion monitoring over 17 years in N = 50 permanent plots distributed across a 1050-ha salt-marsh complex of the European Wadden Sea, we identified clear relationships between salt-marsh vertical growth rates and the soil densities of inorganic and organic carbon. Specifically, we demonstrate a strong positive correlation between vertical accretion and inorganic carbon density while observing a strong negative correlation between vertical accretion and organic carbon density. This decoupling observed between inorganic and organic soil carbon stocks was governed by plant community composition and associated plant traits, which controlled sedimentation processes.

Reservoirs act as carbon sinks when sedimentation of particulate organic carbon (POC) exceeds CO₂ and CH₄ emissions. Here, we study the poorly explored process where phytoplankton-derived acidic polysaccharides (APs) aggregate into particulate organic matter, promoting carbon export to sediments. This source of POC in sediments can mineralize to CO₂ and CH₄ over various timescales. Our research, centered on a Mediterranean reservoir, elucidates phenological trends of APs and POC sedimentation and identifies their predominant drivers. Our findings present synchronic sedimentation patterns of POC and APs but identify a 2-week delay between POC sedimentation and CH₄ emissions. Despite its eutrophic status, our data demonstrate this reservoir's role as a carbon sink, sequestering 4.33 g C m⁻² yr⁻¹. This highlights the need to consider various time scales when quantifying carbon budgets in reservoirs.

Diazotrophs provide a significant reactive nitrogen source in the ocean. Increased warming and stratification may decrease nutrient availability in the future, forcing microbial communities toward using dissolved organic matter (DOM). Not depending on reactive nitrogen availability, diazotrophs may be “winners” in a nutrient-depleted ocean. However, their ability to exploit DOM may influence this success. We exposed cultures of the widespread Crocosphaera to low (26°C, pH 8.1), moderate (28°C, pH 8.0), and extreme (30°C, pH 7.9) climate change scenarios, under control or DOM-amended conditions. Growth was suboptimal in the low and extreme treatments and favored in the moderate treatment. DOM was preferred as a carbon source regardless of the treatment and promoted N₂ fixation in extreme conditions. This was reflected in the increased expression of photosynthesis genes to obtain energy. DOM provides Crocosphaera with a key ecological advantage, possibly dictating diazotroph-derived nitrogen inputs in the future ocean.

The phenology of critical biological events in aquatic ecosystems is rapidly shifting due to climate change. Growing variability in phenological cues can increase the likelihood of trophic mismatches (i.e., mismatches in the timing of peak prey and predator abundances), causing recruitment failures in important fisheries. We assessed changes in the spawning phenology of walleye (Sander vitreus) in 194 Midwest US lakes to investigate factors influencing walleye phenological responses to climate change and associated climate variability, including ice-off timing, lake physical characteristics, and population stocking history. Ice-off phenology shifted earlier, about three times faster than walleye spawning phenology over time. Spawning phenology deviations from historic averages increased in magnitude over time, and large deviations were associated with poor offspring survival. Our results foreshadow the risks of increasingly frequent natural recruitment failures due to mismatches between historically tightly coupled spawning and ice-off phenology.

The Chukchi Sea shelf (CSS) is a highly productive region in the Arctic Ocean and it is highly efficient for absorbing atmospheric carbon dioxide and exporting and retaining carbon in the deep sea. However, with global warming, the carbon retention time in CSS may decrease, leading to less efficient carbon export. Here, we investigate the seasonal variability of carbonate chemistry in CSS using three sets of late- vs. early-summer reoccupations of the same transect. Our findings demonstrate substantially increased and rapid degradation of biologically produced organic matter and therefore acidification over time in the southern CSS due to earlier sea-ice retreat, resulting in significantly shorter carbon retention time. In sharp contrast, no increased degradation has been observed in the northern CSS where photosynthesis has just commenced. In the future, climate change would further diminish the carbon export capacity and exacerbate seasonal acidification not only within CSS but also across other polar coastal oceans.