Shelf Sea Oceanography

1] Shelf seas are an important global carbon sink. In the seasonal thermocline, the subsurface chlorophyll maximum (SCM) supports almost half of summer shelf production. Using observations from the seasonally stratified Celtic Sea (June 2010), we identify wind-driven inertial oscillations as a mechanism for supplying the SCM with the nitrate needed for phytoplankton growth and carbon fixation. Analysis of wind, currents, and turbulent dissipation indicates that inertial oscillations are triggered by a change in the wind velocity. High magnitude, short-lived dissipation spikes occur when the shear and wind vectors align, increasing the daily nitrate flux to the SCM by a factor of at least 17. However, it is likely that the sampling resolution of turbulent dissipation does not always capture the maximum wind-driven peak in mixing. We estimate that wind-driven inertial oscillations supply the SCM with~33% to 71% of the nitrate required for new production in shelf seas during summer. Citation: Williams, C., J. Sharples, C. Mahaffey, and T. Rippeth (2013), Wind-driven nutrient pulses to the subsurface chlorophyll maximum in seasonally stratified shelf seas, Geophys. Res. Lett., 40,

The first decadal-scale reconstruction of British coastal temperature anomalies spanning the last millennium is presented from a sea loch (fjord) basin, Loch Sunart, NW Scotland. Based on modern observation and the results of previous numerical modeling of fjord circulation, benthic foraminiferal oxygen isotope records are interpreted as a record of summer temperature. A significant climate transition, apparently driven by large-scale reorganization of northern Hemisphere atmospheric circulation, occurs in the record around AD 1400. An abrupt, but relatively short-lived climate warming occurs between AD 1540–1610, when the bottom water temperature anomalies are 1.1 °C above the long-term average, which is warmer than most of the 20th century and the late Medieval Warm Period. A long-term cooling occurs throughout the Little Ice Age culminating in the coldest recorded temperature anomalies between the late 1920s and 1940s. The warmest reconstructed temperatures of the past millennium occurred in the last 5 years of the record, which ends in 2006. A replicated post-AD 1900 shift in benthic foraminiferal δ13C of ca −0.6‰ provides evidence of the Oceanic δ13C Suess Effect; this feature provides an independent test of the age model and demonstrates the value of benthic foraminifera as palaeo-proxies in the Loch Sunart record.

1] Near the bottom, the velocity profile in the bottom boundary layer over the continental shelf exhibits a characteristic law-of-the-wall that is consistent with local estimates of friction velocity from near-bottom turbulence measurements. Farther from the bottom, the velocity profile exhibits a deviation from the law-of-the-wall. Here the velocity gradient continues to decrease with height but at a rate greater than that predicted by the law-of-thewall with the local friction velocity. We argue that the shape of the velocity profile is made consistent with the local friction velocity by the introduction of a new length scale that, near the boundary, asymptotes to a value that varies linearly from the bottom. Farther from the boundary, this length scale is consistent with the suppression of velocity fluctuations either by stratification in the upper part of the boundary layer or by proximity to the free surface. The resultant modified law-of-the-wall provides a good representation of velocity profiles observed over the continental shelf when a local estimate of the friction velocity from coincident turbulence observations is used. The modified law-ofthe-wall is then tested on two very different sets of observations, from a shallow tidal channel and from the bottom of the Mediterranean outflow plume. In both cases it is argued that the observed velocity profile is consistent with the modified law-of-the-wall. Implicit in the modified law-of-the-wall is a new scaling for turbulent kinetic energy dissipation rate. This new scaling diverges from the law-of-the-wall prediction above 0.2D (where D is the thickness of the bottom boundary layer) and agrees with observed profiles to 0.6D. Citation: Perlin, A., J. N. Moum, J. M. Klymak, M. D. Levine, T. Boyd, and P. M. Kosro (2005), A modified law-of-the-wall applied to oceanic bottom boundary layers, C10S10 Corresponding values of z 0 are z 0p1 = 0.06 m, z 0p2 = 0.9 m, and z 0' = 0.1 m.

High freshwater inputs into Scottish sea lochs (fjords) combined with the restricted exchange between sea loch basin water and coastal Atlantic water masses are likely to result in reduced regional marine radiocarbon reservoir ages (R[t]) in these environments. To test this hypothesis, historical, museum-archived shells, collected live on known dates prior to AD 1950 from coastal locations in NW Scotland, were14C dated to provide a means of determining R(t) and hence the regional deviation (ΔR) from the modeled global surface ocean reservoir age (R). The sea loch data, when combined with14C dates from the Scottish west coast (Harkness 1983), yield a regional ΔR value of −26 ± 14 yr. The ΔR of sea loch (fjordic) and coastal waters of NW Scotland are statistically different (at a confidence level…

Fjords are glacially over-deepened semi-enclosed marine basins, typically with entrance sills separating their deep waters from the adjacent coastal waters which restrict water circulation and thus oxygen renewal. The location of fjords is principally controlled by the occurrence of ice sheets, either modern or ancestral. Fjords are therefore geomorphological features that represent the transition from the terrestrial to the marine environment and, as such, have the potential to preserve evidence of environmental change. Typically, most fjords have been glaciated a number of times and some high-latitude fjords still possess a resident glacier. In most cases, glacial erosion through successive glacial/interglacial cycles has ensured the removal of sediment sequences within the fjord. Hence the stratigraphic record in fjords largely preserves a glacial-deglacial cycle of deposition over the last 18 ka or so. Sheltered water and high sedimentation rates have the potential to make fjord...

Pronounced seasonal variability, particularly in the surface ocean heat flux, imparts an important control that drives thermal stratification of the tide-dominated middle-and high-latitude shelf seas. Bottom water temperature and salinity data, resolved on a grid 20? latitude by 30? longitude, were combined with a regional synthesis of the salinity:d 18 O relationship in order to generate a spatial and temporal understanding of oxygen isotopes in seawater around the shelf seas of NW Europe. The data are expressed according to equilibrium calcite (d 18 O Eq.calcite ) and, in the shallow mixed water column, exhibit large seasonal changes that are primarily driven by bottom water temperature. Annual bottom water temperature varies from B/38C to /178C in the southern North Sea, generating a seasonal d 18 O Eq.calcite signal of up to 3.2. The amplitude of the seasonal d 18 O Eq.calcite signal is significantly damped (0.1 Á0.2) in deeper, thermally stratified shelf waters. Maps of the monthly distribution d 18 O Eq.calcite provide the first systematic overview of the spatial and temporal changes on the NW European shelf and highlight the importance of understanding seasonal growth on the incorporation of geochemical signatures into marine organisms.

1] Rapidly repeated transects of currents, density, and turbulence through the bottom boundary layer across a relatively uniform stretch of the continental shelf off Oregon reveal the response to a sequence of strong upwelling followed by relaxation and thence a resumption of upwelling. Several definitions of boundary layer thickness are employed to describe the evolution of the bottom boundary layer. Well-mixed and turbulent layers were typically confined to 10 m from the bottom. However, boundary layer thicknesses were greatest during relaxation from upwelling (when mixed layer and turbulent layer thicknesses exceeded 20 m), and turbulence in the bottom boundary layer was most intense at this time. Dense, near-bottom fluid was observed to move upslope with upwelling and back down the slope with relaxation from upwelling. By tracking the intersection of near-bottom isopycnals with the bottom over successive transects, we estimate the cross-shore speed of fluid in the bottom boundary layer. Cross-shore speed agrees well with dynamical estimates of cross-shore velocity in the bottom Ekman layer derived from bottom stress measurements. This leads to a confirmation of the Ekman balance of alongshore momentum in the bottom boundary layer across the full width of the shelf. Good correlation exists between alongshore velocity at the top of the bottom boundary layer and cross-shore velocity of dense fluid in the bottom boundary layer. Application of a derived proxy for bottom stress to moored velocity observations indicates Ekman balance of alongshore momentum at a midshelf location (81 m depth) for a 3 month period in spring/summer 2001. Citation: Perlin, A., J. N. Moum, and J. M. Klymak (2005), Response of the bottom boundary layer over a sloping shelf to variations in alongshore wind,

Marine localities on the west European shelf have been studied to reconstruct the nearshore palaeoceanography of the last two millennia. The sites form a transect from the Iberian margin northeastward via Scotland to western Norway and Iceland. Proxies used for palaeoclimatic reconstructions include stable isotopes, benthic and planktonic foraminfera, diatoms, dinoflagellates, as well as geochemical and sedimentological parameters. Major changes as well as long-term trends in oceanographic conditions are observed in the records, including a general cooling trend through much of the last millennium. There is a clear linkage between the atmospheric processes and the oceanic circulation, and the ocean temperature variability in the records can be correlated with the so-called 'Mediaeval Warm Period' and 'Little Ice Age'. These oscillations are, however, by no means unique within the last two millennia. As an example, sea surface temperatures to the north of Iceland and on the Iberian margin were higher in the Roman Warm Period than at any time during the 'Mediaeval Warm Period'. However, the palaeoceanographic record generally supports a distinct cooling at the transition between the 'Mediaeval Warm Period' and the 'Little Ice Age'. While a number of records indicate a warming of coastal and shelf waters during the last 200 years, the twentieth century does not appear to be unusual when the proxy records spanning the last two millennia are examined.

SINKHOLE ARCO st.69 Lat N 41°59.62', Long E 16°15.15' Depth -73.6 m Recovery 134 cm 22-23 cm Cerastoderma glaucum >41000 yrs uncal BP 95-96 cm Cerastoderma glaucum >42000 yrs uncal BP Limestone with calcisphere and rare plaktonics: Maiolica Fm Chert with intraclasts: Maiolica Fm? Bioclastic rudstone: Ripe Rosse Fm Packstone with planktonic foraminifers and bioclastic: Neogene (cf Pietra Leccese or Calcareniti di Apricena) Polymictic arkosic sandstone Fully marine Pebbles Ensis from ARCO st71 provided an age >41000 yrs uncal BP

Abstract Long-term changes in the state of the Bottom Shelf Water (BSW) on the Western shelf of the Black Sea are assessed using analysis of intra-and inter-annual variations of temperature as well as their relations to physical parameters of both shelf and deep-sea waters. First, large data sets of in-situ observations over the 20th century 5 are compiled into high-resolution monthly climatology at different depth levels. Then, the temperature anomalies from the climatic mean are calculated and aggregated into spatial ...

The south Adriatic shelf offshore of the predominently carbonate Apulian coast is characterized by a peculiar rough topography interpreted as relic karst formed at a time of lower sea level. The study area covers a surface of about 220 km 2 , with depths ranging from 50 to 105 m. The most relevant and diagnostic features are circular depressions a few tens to 150 m in diameter and 0.50 to 20 m deep thought to be dolines at various stages of evolution. The major doline, Oyster Pit, has its top at about 50 m water depth and is 20 m deep. It is partly filled with sediments redeposited by episodic mass failure from the doline's flank. Bedrock samples from the study area document that Plio-Pleistocene calcarenites, tentatively correlated with the Calcarenite di Gravina Fm, are a prime candidate for the carbonate rocks involved in the karstification, although the presence of other units, such as the Peschici or Maiolica Fms, is not excluded. The area containing this subaerial karst landscape was submerged about 12,500 years ago as a result of the postglacial transgression over the continental shelf.

Marine localities on the west European shelf have been studied to reconstruct the nearshore palaeoceanography of the last two millennia. The sites form a transect from the Iberian margin northeastward via Scotland to western Norway and Iceland. Proxies used for palaeoclimatic reconstructions include stable isotopes, benthic and planktonic foraminfera, diatoms, dinoflagellates, as well as geochemical and sedimentological parameters. Major changes as well as long-term trends in oceanographic conditions are observed in the records, including a general cooling trend through much of the last millennium. There is a clear linkage between the atmospheric processes and the oceanic circulation, and the ocean temperature variability in the records can be correlated with the so-called ‘Mediaeval Warm Period’ and ‘Little Ice Age’. These oscillations are, however, by no means unique within the last two millennia. As an example, sea surface temperatures to the north of Iceland and on the Iberian m...

1] Detailed observations of the Ekman spiral in the stratified bottom boundary layer during a 3-month period in an upwelling season over the Oregon shelf suggest a systematic organization. Counter-clockwise veering in the bottom boundary layer is constrained to the weakly stratified layer below the pycnocline, and its height is nearly identical to the turbulent boundary layer height. Veering reaches 13+/À4 degrees near the bottom and exhibits a very weak dependence on the speed and direction of the interior flow and the thickness of the veering layer. A simple Ekman balance model with turbulent viscosity consistent with the law-of-the-wall parameterization modified to account for stratification at the top of the mixed layer is used to demonstrate the importance of stratification on the Ekman veering. The model agrees reasonably well with observations in the lower 60-70% of the bottom mixed layer, above which it diverges from the data due to the unaccounted physics in the interior. Neglect of stratification in an otherwise identical model results in far worse agreement with the data yielding veering in the bottom Ekman layer which is much smaller than measured, but distributed over a much thicker layer.

High freshwater inputs into Scottish sea lochs (fjords) combined with the restricted exchange between sea loch basin water and coastal Atlantic water masses are likely to result in reduced regional marine radiocarbon reservoir ages (R[t]) in these environments. To test this hypothesis, historical, museum-archived shells, collected live on known dates prior to AD 1950 from coastal locations in NW Scotland, were 14 C dated to provide a means of determining R(t) and hence the regional deviation (∆R) from the modeled global surface ocean reservoir age (R). The sea loch data, when combined with 14 C dates from the Scottish west coast (Harkness 1983), yield a regional ∆R value of -26 ± 14 yr. The ∆R of sea loch (fjordic) and coastal waters of NW Scotland are statistically different (at a confidence level >95%) from the ∆R value of 17 ± 14 yr reported for UK coastal waters data after Harkness 1983) and are in good agreement with the coastal ∆R value of -33 ± 93 yr reported by . Therefore, it is recommended that a regional ∆R correction of -26 ± 14 yr should be applied to modern (i.e. pre-bomb but not prehistoric) marine 14 C dates from the NW coast of Scotland.