Multi-year robotic observations reveal the seasonality of downward carbon export pathways in the Southern Ocean

At high latitudes, the export of organic matter from the surface to the ocean interior, the biological carbon pump, has conventionally been attributed to the gravitational sinking of particulate organic carbon (POC). Conspicuous deficits in ocean carbon budgets have recently challenged this long-lived paradigm of a sole pathway. Multiple strands of evidence have demonstrated the importance of additional export pathways, including the particle injection pumps (PIPs). Recent model estimates revealed that PIPs have a comparable downward POC flux to the biological gravitational pump (BGP), but with potentially different seasonal signatures. To date, logistical constraints have prevented concomitant and extensive observations of these pumps, and little is known about the seasonality of their fluxes. Here, using year-round robotic observations and recent advances in optical signal analysis, we concurrently investigated the functioning of two PIPs - the mixed layer and eddy subduction pumps - and the BGP in Southern Ocean waters. By comparing three phytoplankton bloom cycles in contrasting environments, we show how physical forcing and phytoplankton phenology influence the magnitude and seasonality of these pumps, with implications for carbon sequestration efficiency.

Temporal and spatial lags between wind, coastal upwelling, and blue whale occurrence

Understanding relationships between physical drivers and biological response is central to advancing ecological knowledge. Wind is the physical forcing mechanism in coastal upwelling systems, however lags between wind input and biological responses are seldom quantified for marine predators. Lags were examined between wind at an upwelling source, decreased temperatures along the upwelling plume’s trajectory, and blue whale occurrence in New Zealand’s South Taranaki Bight region (STB). Wind speed and sea surface temperature (SST) were extracted for austral spring–summer months between 2009 and 2019. A hydrophone recorded blue whale vocalizations October 2016-March 2017. Timeseries cross-correlation analyses were conducted between wind speed, SST at different locations along the upwelling plume, and blue whale downswept vocalizations (D calls). Results document increasing lag times (0–2 weeks) between wind speed and SST consistent with the spatial progression of upwelling, culminating with increased D call density at the distal end of the plume three weeks after increased wind speeds at the upwelling source. Lag between wind events and blue whale aggregations (n = 34 aggregations 2013–2019) was 2.09 ± 0.43 weeks. Variation in lag was significantly related to the amount of wind over the preceding 30 days, which likely influences stratification. This study enhances knowledge of physical-biological coupling in upwelling ecosystems and enables improved forecasting of species distribution patterns for dynamic management.

Recent trends in air-sea CO2 fluxes and ocean acidification in the Arabian Sea

<p>Recent observations and modeling evidence indicate that the Arabian Sea (AS) is a net source of carbon to the atmosphere. Yet, the interannual variability modulating the air-sea CO<sub>2</sub> fluxes in the region, as well as their long-term trends, remain poorly known. Furthermore, while the rising atmospheric concentration of CO<sub>2</sub> is causing surface ocean pH to drop globally, little is known about local and regional acidification trends in the AS, a region hosting a major coastal upwelling system naturally prone to relatively low surface pH. Here, we simulate the evolution of air-sea CO<sub>2</sub> fluxes and reconstruct the progression of ocean acidification in the AS from 1982 through 2019 using an eddy-resolving ocean biogeochemical model covering the full Indian Ocean and forced with observation-based winds and heat and freshwater fluxes. Additionally, using a set of sensitivity simulations that vary in terms of atmospheric CO<sub>2</sub> levels and physical forcing we quantify the variability of fluxes associated with both natural and anthropogenic CO<sub>2</sub> and disentangle the contributions of climate variability and that of atmospheric CO<sub>2</sub> concentrations to the long-term trends in air-sea CO<sub>2</sub> fluxes and acidification. Our analysis reveals a strong variability in the air-sea CO<sub>2</sub> fluxes and pH on a multitude of timescales ranging from the intra-seasonal to the decadal. Furthermore, a strong progression of ocean acidification with an important penetration into the thermocline is simulated locally near the upwelling regions. Our analysis also indicates that in addition to the increasing anthropogenic CO<sub>2</sub> concentrations in the atmosphere, recent warming and monsoon wind changes have substantially modulated these trends regionally.</p>

Análise do escoamento horizontal de movimento não turbulento na camada limite noturna sob influência de obstruções

When turbulence is well developed, the diffusivity tends to quickly destroy other flow variability modes, so that the turbulent processes become dominant. However, in cases of weak or intermittent turbulence the turbulence scales are restricted to small values, both spatially and temporally. Non-turbulent processes can become important in such cases. This is particularly possible in the Stable Boundary Layer, some studies have focused on non-turbulent flow modes such as submeso, for example. Non-turbulent motions occur simultaneously on other scales and may to dominate the fluctuations of the horizontal flow and vertical flux The physical forcing of submeso flow is still poorly understood, but it is believed to depend significantly on local conditions such as topography and vegetation. The hypothesis assumed in this paper is that obstacles of different nature and dimensions, such as trees, buildings and topography elements affect different flow scales and analyze how turbulent and submeso processes are affected differently.

Evidence for a biological source of widespread, reproducible nighttime oxygen spikes in tropical reef ecosystems has implications for coral health

Primary producers release oxygen as the by-product of photosynthetic light reactions during the day. However, a prevalent, globally-occurring nighttime spike in dissolved oxygen in the absence of light challenges the traditional assumption that biological oxygen production is limited to daylight hours, particularly in tropical coral reefs. Here we show: 1) the widespread nature of this phenomenon, 2) its reproducibility across tropical marine ecosystems, 3) the influence of biotic and abiotic factors on this phenomenon across numerous datasets, and 4) the observation of nighttime oxygen spikes in vitro from incubations of coral reef benthic organisms. The data from this study demonstrate that in addition to physical forcing, biological processes are likely responsible for increasing dissolved oxygen at night. Additionally, we demonstrate an association between these nighttime oxygen spikes and measures of both net community calcification and net community production. These results suggest that nighttime oxygen spikes are likely a biological response associated with increased respiration and are most prominent in communities dominated by calcifying organisms.