Abstract It is a widely held opinion that submarine canyons were cut during the glacial stages of low sea level and now are essentially dormant features, disturbed only on rare occasions by high-speed turbidity currents of torrential proportions. Our research contradicts this concept of the canyons, citing nine years of measurements of currents in the axes of canyons and in other types of seavalleys. Approximately 200 records from continuously operating current meters (during periods of several days to as much as a month) have shown that currents rarely cease flowing alternately up and down the floor of the valleys and frequently attain speeds sufficient to transport sand-sized sediments along the valley axes. Furthermore, turbidity flows with speeds rarely exceeding 3 km/hr are by no means uncommon events and in fact may occur every few days in localities where rivers introduce large quantities of sediment to the sea near the heads of submarine valleys. Our early studies of currents in canyons offshore southern California may have failed to reveal the importance of these low-velocity turbidity currents, partly because here beaches are the chief source of sediment and there are no large (and few small) rivers entering near the canyon heads. Furthermore, the occurrence of turbidity currents would not ordinarily be recorded in many southern California canyons because great masses of kelp and sea grasses are carried downcanyon by the currents, entangling the instruments, stopping their operation, and frequently causing current meters to be swept away. However, in canyons and valley heads off large rivers (or off small rivers during flood conditions) with no kelp debris on the bottom, we found a very different story. In three out of four areas of this sort even our brief periods of current measurement yielded examples of slow turbidity currents, and in the fourth area, off the Fraser delta, the failure to record a turbidity current may have been because of the almost continuous dredging at the river mouth which removes great quantities of available sediment.

Abstract: Spitsbergen Bank is the largest open-shelf cold-water carbonate platform in the Arctic region. Carbonate production is centered around two main carbonate “factories.” The first one, kelp forests growing on the shallowest parts of the platform are the main source area for barnacle sands (i.e., Balanus crenatus). These mobile carbonate sands are transported within a huge clockwise gyre of polar water over the platform. This gives rise to a thin veneer of skeletal sand on the platform interior and carbonate mega-dunes at the margin. At these high latitudes, extreme seasonality is reflected in variation in sea ice cover over the bank and changes in sediment dynamics. Migration of marginal mega-dunes is related to heavy storm events in late autumn/early winter. Smoothing of the dune relief occurs by bottom traction currents through the rest of the year. The second carbonate “factory” is situated on the flanks of the platform, where high productivity conditions are established along the Polar Front at the zone between Atlantic and Arctic water masses. Very efficient bentho-pelagic coupling (e.g., a rapid transfer of planktic food to the benthic communities), accounts for the development of a high biomass. The biota features dense colonies of infaunal bivalves as well as Balanus balanus- hydrozoan- soft coral-sponge-bryozoan buildups. The postglacial succession of cold-water settings on Spitsbergen Bank display a distinct evolutionary trend which highlights variable balances between the main driving forces on cyclically-glaciated carbonate platforms. There is a complete switch-over between the two end-member conditions: maximum drowning and eustatic sea-level lowstands during glacial periods versus maximum efficiency of glacio-isostatic uplift and eustatic sea- level highstand in the Holocene time. These changes in platform configuration are associated with a shift in sedimentary regimes from low-energy, proximal-glaciomarine settings during the glacial and early postglacial period to high-energy, distal-glaciomarine conditions in Holocene time. Evolutionary phases of this shift can be deduced from detailed analysis of facies belts on Spitsbergen Bank and are summarized in a hypothetical model for two successive glacial/interglacial cycles. This model may serve as a reference for the interpretation of fossil counterparts.