We present a week of observations of wave dissipation on the south forereef of Palmyra Atoll. Using wave measurements made in 6.2 m and 11.2 m of water offshore of the surf zone, we computed energy ...fluxes and near‐bottom velocity. Equating the divergence of the shoreward energy flux to its dissipation by bottom friction and parameterizating dissipation in terms of the root‐mean‐square velocity cubed, we find that the wave friction factor, fw, for this reef is 1.80 ± 0.07, nearly an order of magnitude larger than values previously found for reefs. We attribute this remarkably high value of fw to the complex canopy structure of the reef, which we believe may be characteristic of healthy reefs. This suggests that healthy reefs with high coral cover may provide greater coastal protection than do degraded reefs with low coral cover.
Key Points
Shoaling waves observed on a healthy coral reef
Damping of waves is an order of magnitude greater than observed previously
High friction factor observed attributed to canopy flow dynamics
We investigate the functioning of the ocean’s biological pump by analyzing the vertical transfer efficiency of particulate organic carbon (POC). Data evaluated include globally distributed time ...series of sediment trap POC flux, and remotely sensed estimates of net primary production (NPP) and sea surface temperature (SST). Mathematical techniques are developed to compare these temporally discordant time series using NPP and POC flux climatologies. The seasonal variation of NPP is mapped and shows regional‐ and basin‐scale biogeographic patterns reflecting solar, climatic, and oceanographic controls. Patterns of flux are similar, with more high‐frequency variability and a subtropical‐subpolar pattern of maximum flux delayed by about 5 days per degree latitude increase, coherent across multiple sediment trap time series. Seasonal production‐to‐flux analyses indicate during intervals of bloom production, the sinking fraction of NPP is typically half that of other seasons. This globally synchronous pattern may result from seasonally varying biodegradability or multiseasonal retention of POC. The relationship between NPP variability and flux variability reverses with latitude, and may reflect dominance by the large‐amplitude seasonal NPP signal at higher latitudes. We construct algorithms describing labile and refractory flux components as a function of remotely sensed NPP rates, NPP variability, and SST, which predict POC flux with accuracies greater than equations typically employed by global climate models. Globally mapped predictions of POC export, flux to depth, and sedimentation are supplied. Results indicate improved ocean carbon cycle forecasts may be obtained by combining satellite‐based observations and more mechanistic representations taking into account factors such as mineral ballasting and ecosystem structure.
Polar marine ecosystems are particularly vulnerable to the effects of climate change. Warming temperatures, freshening seawater, and disruption to sea‐ice formation potentially all have cascading ...effects on food webs. New approaches are needed to better understand spatiotemporal interactions among biogeochemical processes at the base of Southern Ocean food webs. In marine systems, isoscapes (models of the spatial variation in the stable isotopic composition) of carbon and nitrogen have proven useful in identifying spatial variation in a range of biogeochemical processes, such as nutrient utilization by phytoplankton. Isoscapes provide a baseline for interpreting stable isotope compositions of higher trophic level animals in movement, migration, and diet research. Here, we produce carbon and nitrogen isoscapes across the entire Southern Ocean (>40°S) using surface particulate organic matter isotope data, collected over the past 50 years. We use Integrated Nested Laplace Approximation‐based approaches to predict mean annual isoscapes and four seasonal isoscapes using a suite of environmental data as predictor variables. Clear spatial gradients in δ13C and δ15N values were predicted across the Southern Ocean, consistent with previous statistical and mechanistic views of isotopic variability in this region. We identify strong seasonal variability in both carbon and nitrogen isoscapes, with key implications for the use of static or annual average isoscape baselines in animal studies attempting to document seasonal migratory or foraging behaviors.
Key Points
First carbon and nitrogen isoscape predictions of the entire Southern Ocean, based on particulate organic matter isotope data
Clear spatial gradients in δ13C and δ15N values were predicted, consistent with previously reported isotopic variability in this region
Key implications for the use of isoscape baselines in animal studies attempting to document seasonal migratory or foraging behaviors
•PAH, PCB and PBDE sediment concentrations were studied in Chapala Lake, Mexico.•POP sediment concentrations were indicative of moderate to intense contamination.•POP sediment concentrations can be ...harmful for human through fish consumption.•Despite the banning of POP use, sediment concentrations are still growing since 1990s.•Long-range atmospheric transport has been the main source of POPs to the sediments.
210Pb-dated sediment cores and surface sediments from Lake Chapala (LC), Mexico, were analyzed to assess the temporal trends in concentrations and fluxes of persistent organic pollutants (POPs: PAHs, PCBs and PBDEs). Total sediment concentrations of PAHs (95-1,482 ng g−1), PCBs (9-27 ng g−1) and PBDEs (0.2-2.5 ng g−1) were indicative of moderate to intense contamination. The POP concentrations have progressively increased since the 1990s. The light molecular weight PAHs, and the prevalence of PCB congeners with low-chlorination levels (e.g., di- to tri-CB) and low-to medium-brominated (tri- to penta-BDE) PBDEs in most sections of the sediment profiles, suggested that these POPs have most likely reached these sediments by long-range atmospheric transport from distant sources; although the significant presence of heavier PAH, PCB and PBDE congeners in the topmost sediments, indicate that other nearby and local sources (soil erosion from the catchment, urban and industrial wastewaters discharges, as well as navigation) might have also contributed to the recent input of POPs to LC. Taking into account the relevance of LC as regional freshwater supply and commercial fishing ground, the potential risk posed by the organic contaminated sediments to the biota and human population should not be underestimated.
Antarctic continental shelf waters are the most biologically productive in the Southern Ocean. Although satellite‐derived algorithms report peak productivity during the austral spring/early summer, ...recent studies provide evidence for substantial late summer productivity that is associated with green colored frazil ice. Here we analyze daily Moderate Resolution Imaging Spectroradiometer satellite images for February and March from 2003 to 2017 to identify green colored frazil ice hot spots. Green frazil ice is concentrated in 11 of the 13 major sea ice production polynyas, with the greenest frazil ice in the Terra Nova Bay and Cape Darnley polynyas. While there is substantial interannual variability, green frazil ice is present over greater than 300,000 km2 during March. Late summer frazil ice‐associated algal productivity may be a major phenomenon around Antarctica that is not considered in regional carbon and ecosystem models.
Key Points
Late summer frazil ice‐associated algal blooms are concentrated in major sea ice production polynyas
Green colored frazil ice is present over more than 300,000 km2 during March
Satellite observations show substantial interannual variability in green colored frazil ice extent
Large predators are often highly mobile and can traverse and use multiple habitats. We know surprisingly little about how predator mobility determines important processes of ecosystem connectivity. ...Here we used a variety of data sources drawn from Palmyra Atoll, a remote tropical marine ecosystem where large predators remain in high abundance, to investigate how these animals foster connectivity. Our results indicate that three of Palmyra's most abundant large predators (e.g., two reef sharks and one snapper) use resources from different habitats creating important linkages across ecosystems. Observations of cross-system foraging such as this have important implications for the understanding of ecosystem functioning, the management of large-predator populations, and the design of conservation measures intended to protect whole ecosystems. In the face of widespread declines of large, mobile predators, it is important that resource managers, policy makers, and ecologists work to understand how these predators create connectivity and to determine the impact that their depletions may be having on the integrity of these linkages.
Although reef coral skeletal carbon isotopes (δ
C) are routinely measured, interpretation remains controversial. Here we show results of a consistent inverse relationship between coral δ
C and ...skeletal extension rate over the last several centuries in Porites corals at Fiji, Tonga, Rarotonga and American Samoa in the southwest Pacific. Beginning in the 1950s, this relationship breaks down as the atmospheric
C Suess effect shifts skeletal δ
C > 1.0‰ lower. We also compiled coral δ
C from a global array of sites and find that mean coral δ
C decreases by -1.4‰ for every 5 m increase in water depth (R = 0.68, p < 0.01). This highlights the fundamental sensitivity of coral δ
C to endosymbiotic photosynthesis. Collectively, these results suggest that photosynthetic rate largely determines mean coral δ
C while changes in extension rate and metabolic effects over time modulate skeletal δ
C around this mean value. The newly quantified coral δ
C-water depth relationship may be an effective tool for improving the precision of paleo-sea level reconstruction using corals.
Direct exploitation through fishing is driving dramatic declines of wildlife populations in ocean environments, particularly for predatory and large‐bodied taxa. Despite wide recognition of this ...pattern and well‐established consequences of such trophic downgrading on ecosystem function, there have been few empirical studies examining the effects of fishing on whole system trophic architecture. Understanding these kinds of structural impacts is especially important in coral reef ecosystems—often heavily fished and facing multiple stressors. Given the often high dietary flexibility and numerous functional redundancies in diverse ecosystems such as coral reefs, it is important to establish whether web architecture is strongly impacted by fishing pressure or whether it might be resilient, at least to moderate‐intensity pressure. To examine this question, we used a combination of bulk and compound‐specific stable isotope analyses measured across a range of predatory and low‐trophic‐level consumers between two coral reef ecosystems that differed with respect to fishing pressure but otherwise remained largely similar. We found that even in a high‐diversity system with relatively modest fishing pressure, there were strong reductions in the trophic position (TP) of the three highest TP consumers examined in the fished system but no effects on the TP of lower‐level consumers. We saw no evidence that this shortening of the affected food webs was being driven by changes in basal resource consumption, for example, through changes in the spatial location of foraging by consumers. Instead, this likely reflected internal changes in food web architecture, suggesting that even in diverse systems and with relatively modest pressure, human harvest causes significant compressions in food chain length. This observed shortening of these food webs may have many important emergent ecological consequences for the functioning of ecosystems impacted by fishing or hunting. Such important structural shifts may be widespread but unnoticed by traditional surveys. This insight may also be useful for applied ecosystem managers grappling with choices about the relative importance of protection for remote and pristine areas and the value of strict no‐take areas to protect not just the raw constituents of systems affected by fishing and hunting but also the health and functionality of whole systems.
CO2 sensitivity of Southern Ocean phytoplankton Tortell, Philippe D.; Payne, Christopher D.; Li, Yingyu ...
Geophysical research letters,
February 2008, Letnik:
35, Številka:
4
Journal Article
Recenzirano
Odprti dostop
The Southern Ocean exerts a strong impact on marine biogeochemical cycles and global air‐sea CO2 fluxes. Over the coming century, large increases in surface ocean CO2 levels, combined with increased ...upper water column temperatures and stratification, are expected to diminish Southern Ocean CO2 uptake. These effects could be significantly modulated by concomitant CO2‐dependent changes in the region's biological carbon pump. Here we show that CO2 concentrations affect the physiology, growth and species composition of phytoplankton assemblages in the Ross Sea, Antarctica. Field results from in situ sampling and ship‐board incubation experiments demonstrate that inorganic carbon uptake, steady‐state productivity and diatom species composition are sensitive to CO2 concentrations ranging from 100 to 800 ppm. Elevated CO2 led to a measurable increase in phytoplankton productivity, promoting the growth of larger chain‐forming diatoms. Our results suggest that CO2 concentrations can influence biological carbon cycling in the Southern Ocean, thereby creating potential climate feedbacks.
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