The near‐surface circulation and exchange in the newfoundland grand banks region

Abstract

Analysis of 39 satellite-tracked drifter records from the Newfoundland Grand Banks region has allowed maps of the mean and variable flows to be drawn. The variable currents are particularly large relative to the mean for the shelf, Flemish Cap and in the Newfoundland Basin. The ratio of the mean to variable flow is largest along the path of the Labrador Current. Drifters that either have been released on or migrate onto the Grand Banks remain therefor an average of 71 d. A statistical study of the effect of wind on drifter motion has shown that winds can only account for about 10% of current variability. This result is examined with consideration given to data noise, aliasing and non-stationary conditions. Some drifters that were deployed in the Labrador Current moved onto the shelf and vice versa. These observations have been used to estimate the rate of exchange between the Current and the Grand Banks. Using this exchange rate in a box model, it is calculated that, over the iceberg season, 30% of the bergs will be in the Avalon Channel, 20% on the Grand Banks and 50% in the Labrador Current, in good agreement with the observed distribution. An alternative model based solely on advection is considered as well. The exchange model is also applied to the salinity budget for the Labrador Current with some success. RÉSUMÉ L'étude de 39 relevés provenant de dériveurs suivis par satellite dans la région des Grands bancs de Terre-Neuve a permis de dresser des cartes représentant le courant moyen et ses variabilités. L'intensité des courants variables de la plate-forme continentale, du bonnet flamand et du bassin de Terre-neuve est supérieure à la moyenne. Le rapport entre courant moyen et courant variable est plus important le long de la trajectoire du courant du Labrador. Les dériveurs qu'on rencontre dans la région des Grands bancs y passent en moyenne 71 jours. Une étude statistique de l'effet du vent sur le mouvement des dériveurs a indiqué qu'environ 10 % seulement de la variabilité des courants sont attribuables aux vents. Au moment de l'analyse de ce résultant, on a tenu compte des bruits aléatoires, des problèmes de sous-échantillonnage dans le temps et des conditions non stationnaires. Certains dériveurs du courant du Labrador se sont rendus sur la plate-forme continentale et d'autres ont fait le mouvement inverse. Ces observations ont permis d'estimer le taux d'échange entre le courant et les Grands bancs. En utilisant ce taux d'échange dans le cadre d'un modèle systématique (box model), on calcule que pendant la saison des icebergs, 30 % d'entre eux se trouveront dans le chenal d'Avalon, 20 % sur les Grands bancs et 50 % dans le courant du Labrador, ce qui concorde bien avec la répartition observée. On a également tenu compte d'un autre ATMOSPHERE-OCEAN 23 (3) 1985, 209-227 0705-5900/85/0000-0209S01.25/0 © Canadian Meteorological and Oceanographic Society Downloaded by [5.101.220.201] at 22:50 04 June 2016 210 / Brian Pétrie and Anthony Isenor modèle, basé uniquement sur l'advecticn. Le modèle de Véchange per...

Freshwater export from the Labrador Current to the North Atlantic Current at the Tail of the Grand Banks of Newfoundland

“…Observations indicate that the circulation over the broad, shallow areas of the Grand Banks is weak and highly variable (Petrie and Isenor, 1985;Petrie and Anderson, 1983;Greenberg and Petrie, 1988). However, maps of steric height constructed from historical hydrography suggests that the flow is generally southward and that there might be some seasonality to the flow patterns (Petrie and Anderson, 1983;Csanady, 1979).…”

Seasonality of the inshore Labrador current over the Newfoundland shelf

“…The circulation in this region exhibits significant temporal and spatial variability (Petrie and Anderson, 1983;Narayanan et al, 1996;Loder et al, 1998). The current system has been studied by means of observational data synthesis and numeric modeling efforts (Petrie and Anderson, 1983;Petrie and Isenor, 1985;Greenberg and Petrie, 1988;Sheng and Thompson, 1996;Narayanan et al, 1996;Loder et al, 1998;Han, 2005;Han et al, 2008). The offshore Labrador Current has been investigated in numerous studies because of its climatic significance, e.g., Lazier and Wright, 1993;Eden and Willebrand, 2001;Fischer et al, 2004;Häkkinen and Rhines, 2004;Böning et al, 2006;Dengler et al, 2006, among others, however the inshore Labrador Current over the Newfoundland Shelf has not been fully investigated, especially its seasonality.…”

The freshwater transport of the labrador current

“…For the siope currents the deep flows have standard deviations of about 10 cm 51; for the inshore branch the deep flows have standard deviations of about 3 cm s~. The spectra of the currents (Petrie, 1991;Fissel and Lemon, 1991) show that the subtidai fluctuations have weather band characteristics, so that they wili decorreiate over about a 3-day period, implying that each current record represents (record iength)/(3 days) independent measurements. Thus the standard error of the mean for the deep slope currents (record length~300 days) is about 10 cm ç1/(300/3)1/2 = i cm s and that for the deep inshore branch currents (record iength~100 days) is about 3 cm s-1/(100/3)I/2~0.5 cm s~.…”