Search

Eddy shedding and related biological activity are common features of oceanic eddy formation found in oceanic islands such as the tropical island of Aldabra located in the South Equatorial Current of the Indian Ocean. The occurrence of eddy shedding is in accordance with non-rotating fluid theory and the Reynolds number, leading to the hypothesis that islands at high latitudes exhibit eddy thresholds similar to those predicted in laboratories. While shedding frequency does not correlate indefinitely with the Reynolds number, it does conform with theoretical predictions of Strouhal numbers.

Comparisons between actual observations made at the Drake Passage and the velocity and density fields predicted by the Fine Resolution Antarctic Model (FRAM). The major discrepancies between the observations and the FRAM predictions appear to have arisen due to FRAM's necessary smoothing of topography. Descrepencies found and their implications for equation models for oceanography are discussed.

We have used a coupled ocean–iceberg model to study the variation in global ocean circulation and North Atlantic iceberg flux from 1900 to 2008. The latter component of the study focused particularly on Greenland icebergs feeding into the Labrador Current and past Newfoundland. The model was forced with daily heat, freshwater and wind fluxes from the Twentieth Century Reanalysis. The reanalysis heat fluxes were shown to be offset from the, shorter, NCEP reanalysis and a grid-point correction was applied to this component of the forcing. The model produces a generally realistic ocean circulation, although with an enhanced Atlantic Meridional Overturning largely due to the forcing. The modelled iceberg flux at 48°N is well correlated with the long-term observed flux when using a modelled iceberg discharge that varies in a similar fashion to the highly variable observed flux at 48°N. From this model we infer changes in the spatial and temporal variability of iceberg calving from western Greenland. During the first third of the twentieth century the majority of modelled icebergs reaching 48°N derive from southern Greenland, while only after 1930 is the traditional perspective of a majority of such icebergs originating from Baffin Bay consistent with model results. Decadal-scale changes in the dominant regional sources are found, with oscillations between western Greenland and northern Baffin Bay. The latter origin was modelled to be most important in the last third of the twentieth century, although west Greenland sources have increased in importance in recent years. The model correctly reproduces the pronounced late spring peak in flux at 48°N for southern Greenland icebergs, but has an approximately six month offset for icebergs from Baffin Bay, most likely due to resolution issues leading to model icebergs not being delayed in shallow coastal waters, whereas in reality they may be grounded for some time or trapped in coastal sea-ice. [ABSTRACT FROM AUTHOR]

Abstract: We examine variations in the ice-rafted sources for sediments in the Iceland/East Greenland offshore marine archives by utilizing a sediment unmixing model and link the results to a coupled iceberg-ocean model. Surface samples from around Iceland and along the E/NE Greenland shelf are used to define potential sediment sources, and these are examined within the context of the down-core variations in mineralogy in the <2 mm sediment fraction from a transect of cores across Denmark Strait. A sediment unmixing model is used to estimate the fraction of sediment <2 mm off NW and N Iceland exported across Denmark Strait; this averaged between 10 and 20%. Both the sediment unmixing model and the coupled iceberg-ocean model are consistent in finding that the fraction of “far-travelled” sediments in the Denmark Strait environs is overwhelmingly of local, mid-East Greenland, provenance, and therefore with a significant cross-channel component to their travel. The Holocene record of ice-rafted sediments denotes a three-part division of the Holocene in terms of iceberg sediment transport with a notable increase in the process starting ca 4000 cal yr BP. This latter increase may represent the re-advance during the Neoglacial period of land-terminating glaciers on the Geikie Plateau to become marine-terminating. The contrast in spectral signals between these cores and the 1500-yr cycle at VM28-14, just south of the Denmark Strait, combined with the coupled iceberg-model results, leads us to speculate that the signal at VM28-14 reflects pulses in overflow waters, rather than an ice-rafted signal. [Copyright &y& Elsevier]

Abstract: Icebergs play an important role in climate through the transfer of fresh water and heat between ice sheets and the oceans. Synthetic aperture radar (SAR) images offer a robust way of observing icebergs in the often dark and cloud-covered polar areas. A computer-based technique is proposed to identify icebergs at higher resolution than in the past, allowing the shape of small to medium icebergs to be retained and used for tracking between images acquired at different times. The identification consists of (i) automatic segmentation, followed by (ii) classification of these objects as icebergs or nonicebergs. The classification stage requires user intervention as the icebergs are not always a separable class from other objects, most notably sea ice. The icebergs are then matched between images using their size and shape similarities, and their position tracked. The system performance was assessed by applying the technique to three wintertime ERS-1 PRI images, around Kapp Norvegia (10°W), on the Eastern Weddell Sea coast. The results show both the identification and the tracking to be effective. [Copyright &y& Elsevier]

The presence of widespread terrigenous material of an ice-rafted origin in Quaternary sediments of the Southern Ocean has been recognized for almost 150 years. Normally this material has been ascribed to deposits from icebergs of continental Antarctic origin. However, during Quaternary glaciations there have been periods of extensive land ice across the sub-Antarctic, on both islands scattered around most of the circumpolar extent of the Southern Ocean, as well as in Patagonia, so providing alternative sources for debris-carrying icebergs. Here a relatively high resolution ocean and iceberg model is used to study the potential distribution of ice-rafted debris (IRD) from the range of past ice sources around the Southern Ocean. It is shown that IRD found in marine cores of the Southern Ocean is most likely to have derived from the Antarctic continent in some regions, particularly of the South Atlantic, but that for extensive regions of the Southern Ocean sub-Antarctic sources of IRD, rather than the continent itself, are more likely. This is particularly true equatorward of 55oS, away from the core continental iceberg outflow from the Weddell gyre. It is argued that the glaciated sub-Antarctic cannot be neglected in explaining past IRD records in the Southern Ocean. This has implications not just for reconstructing the history of glaciation in the sub-Antarctic, but also for understanding past variation in the upper ocean circulation within the Quaternary Southern Ocean. [ABSTRACT FROM AUTHOR]

Seasonal coastal upwelling was analyzed along the NW African coastline (11–35°N) from 1981 to 2012. Upwelling magnitudes are calculated by wind speed indices, sea-surface temperature indices and inferred from meteorological station, sea-surface height and vertical water column transport data. A permanent annual upwelling regime is documented across 21–35°N and a seasonal regime across 12–19°N, in accordance with the climatology of previous studies. Upwelling regions were split into three zones: (1) the Mauritania–Senegalese upwelling zone (12–19°N), (2) the strong permanent annual upwelling zone (21–26°N) and (3) the weak permanent upwelling zone (26–35°N). We find compelling evidence in our various indices for the Bakun upwelling intensification hypothesis due to a significant coastal summer wind speed increase, resulting in an increase in upwelling-favorable wind speeds north of 20°N and an increase in downwelling-favorable winds south of 20°N. The North Atlantic Oscillation plays a leading role in modifying interannual variability during the other seasons (autumn–spring), with its influence dominating in winter. The East Atlantic pattern shows a strong correlation with upwelling during spring, while El Niño Southern Oscillation and Atlantic Multi-decadal Oscillation teleconnections were not found. A disagreement between observationally-based wind speed products and reanalysis-derived data is explored. A modification to the Bakun upwelling intensification hypothesis for NW Africa is presented, which accounts for the latitudinal divide in summer wind regimes. [ABSTRACT FROM AUTHOR]