Summertime Bottom Temperatures on the Southeast Shoal of the Grand Bank, and Implications for Exchange Rates

Abstract

Lesder, 1. W. 1991 . Summertime bottom temperatures on the Southeast Shoal of the Grand Bank, and implications for exchange rates. Can. 1. Fish. Aquat. Sci. 48: 131 6-1 3 2 5 .From spring to fall, the Southeast Shoal usually has the warmest bottom water s n the entire Grand Bank s f Newfoundland. Historical hydrographic data indicate that the elevated lower-layer temperatures are derived from the seasonal surface heat input, through vertical exchange across the developing thermocline in combination with the shallow depths of the Shoal. However, in some months, the surface fluxes required by the monthly changes in depth-integrated heat content over the Shoal exceed el irnatological flux estimates computed using bulk formulae, suggesting that the climatoDogical estimates may be low. The seasonal evolution of the lowerlayer temperature provides information on the rates of vertical exchange across the thermocline and horizontal exchange in the lower layer. A seasonal variation in the vertical exchange coefficient, with an approximately inverse relation to the vertical density difference, and significant horizontal exchange in summer are suggested. The associated rates are quantified with a crude axisyrnrnetric model for the lower layer's monthly heat budget.Bu printemps h I'automne, c'est g6nkralement sur le Platier que I'on observe I'eau de fond la plus chaude sur l'ensemble du Grand Bawc de Pere-Neuve. Les donnees hydrographiques recueillies depkeis longtemps indiqkeent que les ternp6ratures eIev6es de la couche inferieure sont caus6es par I'apport saisonnier de chalekgr superficielle, dO 3 B16change vertical au travers de la thermocline qui se dkveloppe, et 2i la faible prsfondeur de ce banc.Toutefois, pendant certains mois, les flux superficiels nkcessaires pour justifier les changements mensuels dans le bilan therrnique integr6 sur la profondeur au-dessus du banc depassent les estimations des flux climatologiques calcul6s 2i I'aide de formules globales, ce qui indiquerait que ces estimations sont peut-Gtre trop faibles. L'6vo-lution saisonni5re de la tempkrature dans la couche inf6rieure donne de I'information sur les taux d'echange vertical en travers de la thermocline et d'kchange horizontal dans la cokeche inferieure. I 1 semblerait exister une variation saisonniere du coefficient dr6change vertical, avec une relation apprsxirnativement inverse 2 la diff6-rence dans la densit6 verticale, et un important echange horizontal en 6t6. Les taux connexes sont quantifies par un rnodele axisymktrique grossier d6crivant le bilan therrnique mensuel de la couche inf6rieure.

The role of air‐sea heat fluxes in annual and interannual ocean temperature variability on the eastern newfoundland shelf

“…Petrie and Anderson, 1983;Greenberg and Petrie, 1988). The excess surface heat fluxes on the central Bank occur primarily in late summer, late fall and early winter which, except for the latter period, is consistent with previous suggestions for peak advective influences (Loder, 1991;Petrie et al, 1991).…”

“…in the mid-pycnocline. The pycnocline values for April-October are in approximate agreement with those estimated for the Southeast Shoal by Loder (1991) using simpler "box" models. The overall average of 5.6 x 10~4 m 2 s" 1 for the central Bank exceeds that for Sta.…”

“…For the central Grand Bank, the only feature that is not consistent with vertical exchange is the intermittency of the cooler near-bottom temperatures. In particular, lower-layer (30-60 m) cooling in August-September, attributed by Loder (1991) to horizontal exchange over the Southeast Shoal, is apparent in Fig. 4a (although such local features are not expected to be fully resolved here).…”

“…Loder, 1991;Petrie et al, 1991), the annual variation of temperature on the eastern Newfoundland Shelf is dominated by summertime near-surface warming resulting in a two-layer system, and fall-winter cooling and deepening of the upper layer to a near-homogeneous water column. This variation has similar features at Sta.…”

Causes of spatio‐temporal variation in the patchiness of larval fish distributions: differential mortality or behaviour?

“…onset of the pelagic phase in this area has been linked to storm-related hydrographic events ) in a manner analogous to the wind-induced hydrographic events which prompt the synchronous release of capelin larvae from beach gravel over large geographical areas inshore . During the period of spawning, egg development and larval existence (summer and fall), a strong pycnocline develops over the Shoal creating a distinct surface and subsurface layer (Loder, 1991). Currents in the two layers are roughly similar in direction and magnitude (Frank et al, 1992).…”