Summertime cooling of the shallow continental shelf

Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): C07015, doi:10.1029/2010JC006744.In summer on the shallow New England continental shelf, near the coast the water temperature is much cooler than the observed surface heat flux suggests. Using depth-integrated heat budgets in 12 and 27 m water depth calculated from observed surface heat flux, water temperature, and velocity, we demonstrate that on time scales of weeks to months the water is persistently cooled due to a mean upwelling circulation. Because the mean wind is weak, that mean circulation is likely not wind driven; it is partly a tidal residual circulation. A feedback exists between the cross-shelf and surface heat fluxes: the two fluxes remain nearly in balance for months, so the water temperature is nearly constant in spite of strong surface heating (the heat budget is two-dimensional). A conceptual model explains the feedback mechanism: the short flushing time of the shallow shelf produces a near steady state heat balance, regardless of the exact form of the circulation, and the feedback is via the influence of surface heating on temperature stratification. Along-shelf heat flux divergence is apparently small compared to the surface and cross-shelf heat flux divergences on time scales of weeks to months. Heat transport due to Stokes drift from surface gravity waves is substantial, warms the shallow shelf in summer, and was previously ignored. In winter, the surface heat flux dominates and the observed water temperature is close to the temperature predicted from surface cooling (the heat budget is one-dimensional); weak winter stratification makes the cross-shelf heat flux small even during strong cross-shelf circulation.This research was funded by National Aeronautics and Space Administration Headquarters grant NNG04GL03G and Earth System Science Fellowship Grant NNG04GQ14H; Woods Hole Oceanographic Institution through Academic Programs Fellowship Funds and MVCO; National Science Foundation grants OCE‐0241292, OCE‐0548961, and OCE‐0337892; the Jewett/ EDUC/Harrison Foundation; and Office of Naval Research contracts N00014‐01‐1‐0029 and N00014‐05‐10090 for the Low‐Wind Component of the Coupled Boundary Layers Air‐Sea Transfer Experiment

Application of the Beer–Lambert Model to Attenuation of Photosynthetically Active Radiation in a Shallow, Eutrophic Lake

Models of primary production in aquatic systems must include a means to estimate subsurface light. Such models often use the Beer–Lambert law, assuming exponential attenuation of light with depth. It is further assumed that the diffuse attenuation coefficient may be estimated as a summation of scattering/absorbing constituent concentrations multiplied by their respective specific attenuation coefficients. While theoretical deviations from these assumptions have been documented, it is useful to consider the empirical performance of this common approach. Photosynthetically active radiation (PAR) levels and water quality conditions were recorded weekly from six to eight monitoring stations in western Lake Erie between 2012 and 2016. Exponential PAR extinction models yielded a mean attenuation coefficient of 1.55 m (interquartile range = 0.74–1.90 m). While more complex light attenuation models are available, analysis of residuals indicated that the simple Beer–Lambert model is adequate for shallow, eutrophic waters similar to western Lake Erie (R2 > 0.9 for 96% of samples). Three groups of water quality variables were predictive of PAR attenuation: total and nonvolatile suspended particles, dissolved organic substances (dissolved organic carbon and chromophoric dissolved organic matter), and organic solids (volatile suspended solids and chlorophyll). Multiple regression models using these variables predicted 3–90% of the variability in PAR attenuation, with a median adjusted R2 = 0.86. Explanatory variables within these groups may substitute for each other while maintaining similar model performance, indicating that various combinations of water quality variables may be useful to predict PAR attenuation, depending on availability within a model framework or monitoring program.Key PointsThe Beer–Lambert law effectively models photosynthetically active radiation in western Lake Erie, despite some systematic deviationsField‐obtained water quality parameters can predict photosynthetically active radiation attenuation with a high degree of confidenceSuspended particle concentration is most predictive of photosynthetically active radiation attenuation in this turbid, eutrophic basinPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/147097/1/wrcr23654_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/147097/2/wrcr23654-sup-0001-2018WR023024-SI.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/147097/3/wrcr23654.pd

Atmosphere-ocean coupled processes in the Madden-Julian oscillation

The Madden-Julian oscillation (MJO) is a convectively coupled 30-70 day (intraseasonal) tropical atmospheric mode that drives variations in global weather, but which is poorly simulated in most atmospheric general circulation models. Over the past two decades, field campaigns and modeling experiments have suggested that tropical atmosphere-ocean interactions may sustain or amplify the pattern of enhanced and suppressed atmospheric convection that defines the MJO, and encourage its eastward propagation through the Indian and Pacific Oceans. New observations collected during the past decade have advanced our understand of the ocean response to atmospheric MJO forcing and the resulting intraseasonal sea surface temperature (SST) fluctuations. Numerous modeling studies have revealed a considerable impact of the mean state on MJO ocean-atmosphere coupled processes, as well as the importance of resolving the diurnal cycle of atmosphere--upper-ocean interactions. New diagnostic methods provide insight to atmospheric variability and physical processes associated with the MJO, but offer limited insight on the role of ocean feedbacks. Consequently, uncertainty remains concerning the role of the ocean in MJO theory. Our understanding of how atmosphere-ocean coupled processes affect the MJO can be improved by collecting observations in poorly sampled regions of MJO activity, assessing oceanic and atmospheric drivers of surface fluxes, improving the representation of upper-ocean mixing in coupled-model simulations, designing model experiments that minimize mean-state differences, and developing diagnostic tools to evaluate the nature and role of coupled ocean-atmosphere processes over the MJO cycle

Ultraviolet polarisation sensitivity in the stomatopod crustacean Odontodactylus scyllarus

The ommatidia of crustacean eyes typically contain two classes of photoreceptors with orthogonally oriented microvilli. These receptors provide the basis for two-channel polarisation vision in the blue–green spectrum. The retinae of gonodactyloid stomatopod crustaceans possess a great variety of structural specialisations for elaborate polarisation vision. One type of specialisation is found in the small, distally placed R8 cells within the two most ventral rows of the mid-band. These ultraviolet-sensitive photoreceptors produce parallel microvilli, a feature suggestive for polarisation-sensitive photoreceptors. Here, we show by means of intracellular recordings combined with dye-injections that in the gonodactyloid species Odontodactylus scyllarus, the R8 cells of mid-band rows 5 and 6 are sensitive to linear polarised ultraviolet light. We show that mid-band row 5 R8 cells respond maximally to light with an e-vector oriented parallel to the mid-band, whereas mid-band row 6 R8 cells respond maximally to light with an e-vector oriented perpendicular to the mid-band. This orthogonal arrangement of ultraviolet-sensitive receptor cells could support ultraviolet polarisation vision. R8 cells of rows 5 and 6 are known to act as quarter-wave retarders around 500 nm and thus are the first photoreceptor type described with a potential dual role in polarisation vision

Aggressive communication in aquatic environments

© 2019 The Author. Functional Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Society. Aggressive interactions are ubiquitous among animals. They are either directed towards heterospecifics, like predators or competitors, or conspecifics. During intraspecific encounters, aggression often serves to establish hierarchies within the social group. Thus, in order to understand the mechanisms mediating social organization, it is important to comprehend the escalation and avoidance of aggressive behaviour. Overt aggressive interactions are costly not only in terms of increased risk of injury or death, but also due to opportunity costs and energy expenditure. In order to reduce these costs, animals are expected to communicate their strength and aggressive motivation prior to fights. For this purpose, they use different means of communication in various sensory modalities, that is visual, acoustic, chemical, mechanosensory and electric cues. These different modalities can convey different or similar information, underlining the importance of understanding the multimodal communication of aggression. Thus far, most studies on signalling during aggressive encounters have focussed on visual or acoustic cues, most likely as these are the two modalities predominantly used by humans. However, depending on the species’ ecology, visual or acoustic cues might play a minor role for many species. Especially in aquatic systems, visual communication is often hampered due to high levels of turbidity or limited light conditions. Here, alternative modalities such as chemical, mechanical or electrical cues are expected to play a prominent role. In this review, I provide an overview of different modalities used during aggressive communication in aquatic organisms. I highlight the importance of studying the role of multimodal communication during aggressive encounters in general and discuss the importance of understanding aquatic communication in the light of conservation and animal welfare issues

Living on Cold Substrata: New Insights and Approaches in the Study of Microphytobenthos Ecophysiology and Ecology in Kongsfjorden

Organisms in shallow waters at high latitudes are under pressure due to climate change. These areas are typically inhabited by microphytobenthos (MPB) communities, composed mainly of diatoms. Only sparse information is available on the ecophysiology and acclimation processes within MPBs from Arctic regions. The physico-chemical environment and the ecology and ecophysiology of benthic diatoms in Kongsfjorden (Svalbard, Norway) are addressed in this review. MPB biofilms cover extensive areas of sediment. They show high rates of primary production, stabilise sediment surfaces against erosion under hydrodynamic forces,and affect the exchange of oxygen and nutrients across the sediment-water interface. Additionally, this phototrophic community represents a key component in the functioning of the Kongsfjorden trophic web, particularly as a major food source for benthic suspension- or deposit-feeders. MPB in Kongsfjorden is confronted with pronounced seasonal variations in solar radiation, low temperatures, and hyposaline (meltwater) conditions in summer, as well as long periods of ice and snow cover in winter. From the few data available, it seems that these organisms can easily cope with these environmental extremes. The underlying physiological mechanisms that allow growth and photosynthesis to continue under widely varying abiotic parameters, along with vertical migration and heterotrophy, and biochemical features such as a pronounced fatty-acid metabolism and silicate incorporation are discussed. Existing gaps in our knowledge of benthic diatoms in Kongsfjorden, such as the chemical ecology of biotic interactions, need to be filled. In addition, since many of the underlying molecular acclimation mechanisms are poorly understood, modern approaches based on transcriptomics, proteomics, and/or metabolomics, in conjunction with cell biological and biochemical techniques, are urgently needed. Climate change models for the Arctic predict other multifactorial stressors, such as an increase in precipitation and permafrost thawing, with consequences for the shallow-water regions. Both precipitation and permafrost thawing are likely to increase nutrient-enriched, turbid freshwater runoff and may locally counteract the expected increase in coastal radiation availability. So far, complex interactions among factors, as well as the full genetic diversity and physiological plasticity of Arctic benthic diatoms, have only rarely been considered. The limited existing information is described and discussed in this review