Resuspension by fish facilitates the transport and redistribution of coastal sediments

Author Posting. © Association for the Sciences of Limnology and Oceanography, 2012. This article is posted here by permission of Association for the Sciences of Limnology and Oceanography for personal use, not for redistribution. The definitive version was published in Limnology and Oceanography 57 (2012): 945-958, doi:10.4319/lo.2012.57.4.0945.Oxygen availability restricts groundfish to the oxygenated, shallow margins of Saanich Inlet, an intermittently anoxic fjord in British Columbia, Canada. New and previously reported 210Pb measurements in sediment cores compared with flux data from sediment traps indicate major focusing of sediments from the oxygenated margins to the anoxic basin seafloor. We present environmental and experimental evidence that groundfish activity in the margins is the major contributor to this focusing. Fine particles resuspended by groundfish are advected offshore by weak bottom currents, eventually settling in the anoxic basin. Transmittance and sediment trap data from the water column show that this transport process maintains an intermediate nepheloid layer (INL) in the center of the Inlet. This INL is located above the redox interface and is unrelated to water density shifts in the water column. We propose that this INL is shaped by the distribution of groundfish (as resuspension sources) along the slope and hence by oxygen availability to these fish. We support this conclusion with a conceptual model of the resuspension and offshore transport of sediment. This fish-induced transport mechanism for sediments is likely to enhance organic matter decomposition in oxygenated sediments and its sequestration in anoxic seafloors.The VENUS Project and University of Victoria supported the ship and submersible time for field experiments, and the U.S. Geological Survey and Coastal and Marine Geological Program generously supported J.C. The project was supported by Discovery Grants from the Natural Sciences and Engineering Research Council of Canada to V.T. and P.S. and a Yohay Ben-Nun fellowship and Moshe Shilo Center for Marine Biogeochemistry Fund award to T.K

Marine oligotrophication due to fine sediments and nutrient starvation caused by anthropogenic sediment and water retention in large rivers: the Nile damming case

In the last two centuries, human activities have radically reduced the transport of suspended sediment and water to marine systems, mainly in the northern hemisphere, while complete sediment retention has been reported for the Nile River after the construction of the Aswan High Dam (AHD). Here, we focused on changes in the inner-shelf sediments most exposed to the pre-AHD flood plume in the distal part of its littoral cell as a predictor of the ecological response to large river fragmentation. Substantial reductions in fine (15-40%) and increases in coarse (~8 fold) sediment accumulation rates, increases in CaCO3 (~50%), decreases in autochthonous and total organic carbon (OC), and changes in the benthic foraminiferal assemblage toward more OC-sensitive species suggest an enhanced oligotrophication trend. The reduced nutrient fluxes and OC accumulation, and the coarsening of the shelf sediments inhibit the retention of “blue” carbon. Combined with fast climate warming and salinization, river fragmentation may have essential implications for the Eastern Mediterranean ecosystem via benthic oligotrophication processes

Groundfish overfishing, diatom decline, and the marine silica cycle : lessons from Saanich Inlet, Canada, and the Baltic Sea cod crash

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 23 (2009): GB4032, doi:10.1029/2008GB003416.In this study, we link groundfish activity to the marine silica cycle and suggest that the drastic mid-1980s crash of the Baltic Sea cod (Gadus morhua) population triggered a cascade of events leading to decrease in dissolved silica (DSi) and diatom abundance in the water. We suggest that this seemingly unrelated sequence of events was caused by a marked decline in sediment resuspension associated with reduced groundfish activity resulting from the cod crash. In a study in Saanich Inlet, British Columbia, Canada, we discovered that, by resuspending bottom sediments, groundfish triple DSi fluxes from the sediments and reduce silica accumulation therein. Using these findings and the available oceanographic and environmental data from the Baltic Sea, we estimate that overfishing and recruitment failure of Baltic cod reduced by 20% the DSi supply from bottom sediments to the surface water leading to a decline in the diatom population in the Baltic Sea. The major importance of the marginal ocean in the marine silica cycle and the associated high population density of groundfish suggest that groundfish play a major role in the silica cycle. We postulate that dwindling groundfish populations caused by anthropogenic perturbations, e.g., overfishing and bottom water anoxia, may cause shifts in marine phytoplankton communities.We acknowledge the VENUS Project, University of Victoria, for supporting the ship and submersible time for field experiments and USGS, CMGP, for support to J.C. Additional funding from NSERC Canada and from the Canada Research Chairs Foundation to V.T.; a Rothschild fellowship to G.Y.; and a Yohay Ben-Nun fellowship and Moshe Shilo Center for Marine Biogeochemistry fund to T.K. are also acknowledged

Offshore Evidence for an Undocumented Tsunami Event in the 'Low Risk' Gulf of Aqaba-Eilat, Northern Red Sea.

Although the Gulf of Aqaba-Eilat is located in the tectonically active northern Red Sea, it has been described as low-risk with regard to tsunami activity because there are no modern records of damaging tsunami events and only one tsunami (1068 AD) referred to in historical records. However, this assessment may be poorly informed given that the area was formed by and is located along the seismically active Dead Sea Fault, its population is known to fluctuate in size and literacy in part due to its harsh hyper-arid climate, and there is a dearth of field studies addressing the presence or absence of tsunamigenic deposits. Here we show evidence from two offshore cores for a major paleotsunami that occurred ~2300 years ago with a sedimentological footprint that far exceeds the scarce markers of the historically mentioned 1068 AD event. The interpretation is based on the presence of a laterally continuous and synchronous, anomalous sedimentological deposit that includes allochtonous inclusions and unique structural characteristics. Based on sedimentological parameters, these deposits could not be accounted for by other transport events, or other known background sedimentological processes

P fluxes and prokaryotic cycling at benthic boundary layer in the deep southeastern Mediterranean Sea

The sediment-water interface is a site of active nutrients exchange between the geosphere and the hydrosphere. We quantified fluxes of dissolved inorganic and organic phosphorous between the deep sediments and the overlying waters of the P-limited southeastern Mediterranean Sea (SEMS) using sediment core incubations. Sediments were collected throughout the Israeli exclusive economic zone and analyzed for their pore-water physicochemical characteristics. We also designed custom-made incubation flux chambers and followed dissolved inorganic and organic phosphorous dynamics as well as prokaryotic microbial activity in the overlying waters for several days. We show that due to the low organic matter content and the well-oxygenated conditions, the sediments of the SEMS function as a PO4 sink. The sedimentary net removal flux of P is equal to a turnover time of ~90 years, similar to the deep water residence time in this basin, hence contributing to the low concentration of PO4 in the deep water of the SEMS. Our incubation experiments show that aside from abiotic processes, such as, adsorption and co-precipitation of PO4, prokaryotic microbial activity play a pivotal role in P-recycling, resulting in a flux of dissolved organic P (DOP) to the overlaying. Organic molecules containing P and C are a known limiting factor for bacteria, and upon release from the sediment stimulated increased prokaryotic microbial activity. Our results highlight the role of the seabed as a hot-spot for microbial activity