United States Senate Inquiry

Day 17

Memorandum in re Drift of Ice On or Near the Grand Banks

(Submitted by the Hydrographic Office May 13, 1912.)

1. The Labrador Current, which brings both berg and field ice down past Newfoundland, sweeps across the banks in a generally south to southwest direction, flowing more westerly on its surface as it approaches the warm Gulf Stream water in about latitude 43°, with a set of about 12 miles a day. The speed of the Gulf Stream drift at its northern edge is only about 6 miles a day at the fiftieth meridian and its depth is probably less than 300 feet.

2. An ice-field arriving at the edge of the Gulf Stream drift finds itself impelled less and less to southward and more and more to eastward and north-eastward; but a deeply floating iceberg may continue to plow southward into the warm east-flowing current and end its career south of latitude 40°; by melting and breaking up. The reason for this is that the cold, south-moving current actually under-runs the warm surface water.

3. The southward progress of icebergs across the Grand Flanks is estimated to be a degree in five days, or about 12 miles a day; but it seems to slack up as the warm current near the tail of the bank is approached (lat. 42°; to 44°; N., long. 49°; to 51°; W.) Here the icebergs are reported with greatest frequency. This may be because the largest number of passing steamers travels the region or because the bergs loitering that vicinity owing to the commingling of the two ocean currents above named.

4. The course of an iceberg in that region could be predicted if the following factors in the problem were known: (a) Vertical section below water. (b) what ratio of the vertical section is in each current (polar and Gulf Stream), (c) direction of each current. (d) velocity of each current. What these factors are must be estimated in each case, varying with each berg according shape and size, and varying with the location and date to some extent. 5. Not much is known regarding the subsurface current. This should be studied during a hydrographic survey of the banks: at the same time careful observations are needed of the surface currents (direction, velocity, meeting points, temperature, color, etc.). A thorough study of the question is desirable; and it would be possible for a naval vessel to gain much useful information by a season's work in that vicinity (April to August, inclusive). She could also record direct observations of ice movements, and act an a radiotelegraph station to warn other ships.

JOHN J. KNAPP, Captain.
United States Navy, Hydrographer.