of travel. In the period shortly following release, 

 cards may have been more responsive to changes in 

 wind direction than to the direction and velocity of 

 surface-water movements. Movements of these 

 cards can therefore be interpreted as only rough ap- 

 proximations of surface-water movements. Despite 

 their shortcomings as current indicators, some specu- 

 lation may be permitted about the possible circula- 

 tion patterns that may have influenced the drift of 

 cards between release and recovery points. 



Drift cards released at station 4 on July 8, 1953 

 (fig. 12), were first recovered south of the release 

 point on the west shore of Keweenaw Bay and next 

 on the south shore of the bay. Later recoveries along 

 the south shore of Lake Superior point toward an 

 easterly littoral current in this area as indicated by 

 work of Harrington (1895) and Ruschmeyer, Olson, 

 and Bosch (1957). Subsequent recoveries along the 

 west shore north of the point of release indicate, 

 however, that only a few cards entered this littoral 

 current. This movement verifies the inference of 

 Ruschmeyer, Olson, and Bosch that a fairly well 

 defined current moves south from the tip of the 

 peninsula to the south shore, and that mixing of this 

 current with bay water is limited (their drift bottles 

 moved from the tip of the Keweenaw Peninsula to the 

 south shore but no recoveries were made in Keweenaw 

 Bay). The large number of cards retained within 

 the bay in this study strongly suggest a well defined 

 eddy with a counterclockwise rotation in at least 

 the southern portion of the bay. 



Cards released at station 48 on July 3, 1953 

 (fig. 7), were first recovered 9 days later near the 

 tip of the Keweenaw Peninsula. The short straight- 

 line distance between the points of release and re- 

 covery suggests that the cards may have moved in 

 an eddy just southeast of the peninsula's tip for a 

 short time before they were washed ashore. If so, 

 this eddy is probably small and moves in a clockwise 

 direction in conformance with the southward current 

 from the tip of the peninsula (Ruschmeyer, Olson, 

 and Bosch 1957) and the westward movement of 

 water in central Keweenaw Bay (fig. 12) discussed 

 in the preceding paragraph. Subsequent recoveries 

 on all sides of Manitou Island indicate an eddy 

 around the island, and indeed a possible area 



of mixing with the littoral current flowing eastward 

 off the tip of the Keweenaw Peninsula. Drift bottles 

 carried in this current have been recovered on 

 this island (Ruschmeyer, Olson, and Bosch 1957). 

 Some drift cards, however, crossed this current 

 and entered the circulation of the open lake to 

 be recovered some 2 months after release on the 

 north and east shore of the lake (fig. 7). These cards 

 may have traveled northeast across the lake, and 

 split into two groups west cf Michipicoten Island to 

 give the widely separated recovery locations near 

 Marathon and Michipicoten, Ontario. It is possible, 

 however, that the cards that landed near Michipicoten 

 were part of a group carried in the current flowing 

 south from the tip of the Keweenaw Peninsula and that 

 they moved to their recovery point in the counter- 

 clockwise flow of rile eastern basin of the lake. 



Drift cards were released in the open lake between 

 the Keweenaw Peninsula and Isle Royale at BT cast 

 IV-34 and stations 11 and 49 on July 4 and 7, 1953 

 (figs. 8, 9, 11). On the dates of release, stations 11 

 and 49 were outside the littoral current that flows 

 easterly along the north shore of the Keweenaw Penin- 

 sula. The recovery of cards from all of those releases 

 exclusively along the north-central shore of the lake 

 reflects a possible counterclockwise circulation with- 

 in the north-central basin during the period of this 

 study. If the circulation in the central and eastern 

 basins during this period had made up a single mas- 

 sive eddy, as suggested by Harrington's (1895) work, 

 at least some of the drift cards would have been car- 

 ried into the eastern basin. 



Cards released near the lip of the Keweenaw 

 Peninsula (station 49, fig. 8) were apparently in- 

 fluenced by the outer edge of a water mass rotating 

 coimterclockwise in the north-central basin. This 

 influence would account for the returns along the 

 northeast shore of the central basin. Cards released 

 with BT cast IV-34 (fig. 9) and at station 11 (fig. 11) 

 appear to have entered this circulation and were more 

 widely dispersed before they came ashore. Earliest 

 recovery dates for both of these releases were nearly 

 the same over the entire area where they came to 

 shore. Recovery dates of cards released with BT 

 cast IV-34 do, however, show a slight progression 

 from east to west. 



21 



