Limnology and Oceanography Letters最新文献

Shallow-water hydrothermal vents have gained growing attention for their intricate characteristics caused by various epipelagic factors. The shallow-water hydrothermal system offshore Kueishan Island, Taiwan, situated in an earthquake-prone area, has prompted our exploration into the relationship between hydrothermal and seismic activities. Our 2-yr observation uncovered that the hydrothermal venting entered a silent period in November 2020, followed by a resurgence of activity after September 2021, coinciding with high-frequency shallow earthquakes occurring within 5 km of the vents. The pH level, dissolved inorganic carbon, alkalinity, pCO₂, $��{\mathrm{CO}}_3^{�2�-�}�$, and sulfide served as indicators of hydrothermal activity, contributing to environmental changes in habitats during period transition. However, peering physicochemical and soundscape conditions, distinctions may still arise during two separate active periods. Through multivariate analysis, this study highlights the variability of shallow-water hydrothermal vents, emphasizing the necessity for more frequent and detailed investigations to further understand these extreme and dynamic marine ecosystems.

Reliable high-resolution, pre-observational-period sea-ice datasets are rare but critical for contextualizing recent sea-ice declines and future scenarios. We combine sedimentary ancient DNA of the sea-ice dinoflagellate Polarella glacialis (Pgla-sedaDNA) with selected highly branched isoprenoid (HBI) biomarkers alongside other indicators to reconstruct sub-decadal sea-ice changes in a marine archive from the Antarctic Peninsula that extends to ~ 1900 CE. Pre-1940 CE, the continuously present sea-ice biomarker IPSO₂₅ yet absent Pgla-sedaDNA, along with low open-water biomarkers and total organic carbon (TOC), imply more prominent seasonal sea ice and lower productivity under cooler climate. Post-1940 CE, rising Pgla-sedaDNA and open-water HBIs under climate warming reflect young ice with a retreating sea-ice edge. Over the last two decades, lower Pgla-sedaDNA, higher open-water HBIs and TOC infer known warming, sea-ice reduction, and increased productivity. Our multiproxy-based palaeo-histories agree well with observational data, highlighting the potential of this combination of proxies for nuanced and long-term sea-ice reconstructions.

Although seagrasses are expected to thrive in future acidified oceans by overcoming low CO₂ diffusion into plant tissues, the co-occurrence of environmental stressors may affect their growth. Volcanic CO₂ vents are often associated with toxic gases and metal-rich fluids representing ideal sites to assess the effects of multiple stressors. We evaluated the response of Posidonia oceanica growing near shallow CO₂ vents characterized by H₂S spill-out by comparing meadow structure and phenology to an area with no gas emissions. Seagrass descriptors at meadow, shoot and leaf level indicated that P. oceanica experienced stressful conditions at the vent area, in clear contrast to the flourishing features of P. oceanica previously described at CO₂ vents with no evidence of toxic inputs. Furthermore, the reduction in both leaf δ³⁴S and growth at the vent area indicates that sulfide intrusion occurs and affects seagrass growth performance, dampening the expected beneficial effects of high CO₂ levels.

In this study, we explored the realized thermal sensitivities of various phytoplankton groups in natural seawater, a crucial aspect for understanding the dynamics of marine ecosystems under climate change. Utilizing a decadal pigment dataset (2002–2015) from China Seas and employing generalized additive mixed models coupled with maximum entropy modeling, we discerned thermal sensitivity differentiations among nine phytoplankton groups, encompassing the full-size spectrum. Our findings revealed that cryptophytes were exceptionally thermally sensitive, with a strong correlation between temperature changes and biomass variance. Characterized by a preference for cooler waters, cryptophytes had a low mean temperature niche and a narrow niche breadth. Notably, they exhibited the lowest temperature tipping point, highlighting their heightened vulnerability to warming trends. These findings underscored the significance of cryptophytes, an often-overlooked group, in understanding ecosystem responses to climate shifts, and emphasized their potential role as key indicators in marine ecological studies under global warming.

Streams are significant emitters of carbon dioxide (CO₂) to the atmosphere that are influenced by diel CO₂ dynamics. However, we know little about diel CO₂ variability within streams, the diel dynamics of CO₂ in the air above streams, and the consequences for emission calculations. We studied five pre-alpine streams by equipping three sites per stream in close proximity (~ 1 km apart) with automatic logging stations that continuously recorded water and air CO₂ partial pressures (pCO₂) for 2–4 d. All streams and sites showed increased pCO₂ at night and decreased pCO₂ during the day, however, with fourfold higher diel amplitudes for atmospheric pCO₂ compared to the water. Calculating diffusive CO₂ fluxes with fixed compared to dynamic measured atmospheric CO₂ resulted in negligible to 431% lower estimates. We might thus currently overestimate fluvial CO₂ emissions and should include diel water and air CO₂ variability to more accurately assess stream CO₂ emissions.

Terrestrial groundwater travels through subterranean estuaries before reaching the sea. Groundwater-derived nutrients drive coastal water quality, primary production, and eutrophication. We determined how dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), and dissolved organic nitrogen (DON) are transformed within subterranean estuaries and estimated submarine groundwater discharge (SGD) nutrient loads compiling > 10,000 groundwater samples from 216 sites worldwide. Nutrients exhibited complex, nonconservative behavior in subterranean estuaries. Fresh groundwater DIN and DIP are usually produced, and DON is consumed during transport. Median total SGD (saline and fresh) fluxes globally were 5.4, 2.6, and 0.18 Tmol yr⁻¹ for DIN, DON, and DIP, respectively. Despite large natural variability, total SGD fluxes likely exceed global riverine nutrient export. Fresh SGD is a small source of new nutrients, but saline SGD is an important source of mostly recycled nutrients. Nutrients exported via SGD via subterranean estuaries are critical to coastal biogeochemistry and a significant nutrient source to the oceans.

Giant kelp (Macrocystis pyrifera) forests are common along the California coast. Attached on the rocky bottom at depths of approximately 5–25 m, the kelp, when mature, spans the water column and develops dense, buoyant canopies that interact with waves and currents. We present two novel results based on observations of surface gravity waves in a kelp forest in Point Loma, California. First, we report short wave (1–3 s) attenuation in kelp, quantified by an exponential decay coefficient $��\alpha �\sim �O�\left(�{10}^{�-�3�}�m^{�-�1�}�\right)�$—comparable to the dampening effect of sea ice. Second, we identify seasonal and tidal changes in attenuation, peaking mid-summer with maximum kelp cover, and during low tide when a greater proportion of the fronds are at the surface. Thus, the naturally occurring surface canopies of kelp forests can act as temporally varying, high-frequency filters of wave energy.

Biodiversity generally increases productivity in ecosystems; however, this is mediated by the specific functional traits that come with biodiversity loss or gain and how these traits interact with environmental conditions. Most biodiversity studies evaluate the effects of species richness alone, despite our increasing understanding that intraspecific diversity can have equally strong impacts. Here, we manipulate both species richness and intraspecific richness (i.e., number of distinct strains) in marine diatom communities to explicitly test the relative importance of species and strain richness for biomass and trait diversity in six distinct temperature/nutrient environments. We show that species and strain richness both have significant effects on biomass and growth rates, but more importantly, they interact with each other, indicating that cross-species diversity effects depend on within-species diversity and vice versa. This intertwined relationship thus calls for more integrative approaches quantifying the relative importance of distinct biodiversity components and environmental context on ecosystem functioning.

The (sub)tropical western North Pacific is potentially an area of intense nitrogen (N₂) fixation in the global ocean, despite limited understanding of the flux and controlling factors. We conducted high-resolution observations from 2016 to 2021 in this region and used machine learning algorithms to simulate N₂ fixation flux. Models estimated an N₂ fixation flux from 5.72 to 6.45 Tg N yr⁻¹, with strong seasonal variation and peak rates in summer. The western North Pacific Subtropical Gyre and the Kuroshio Current contributed more to N₂ fixation flux than did the adjacent areas. Models suggested that sea surface temperature, photosynthetically available radiation, and nutrient supply were most strongly correlated with seasonal and spatial variations in N₂ fixation. This study provides an improved estimation of N₂ fixation in the western North Pacific and advances our understanding of its role in ocean productivity.