LATE WISCONSINAN TO PRESENT SEDIMENTATION OF ORGANIC-MATTER OFF NORTHERN NEWFOUNDLAND IN RESPONSE TO CLIMATOLOGICAL EVENTS

Carbon and nitrogen isotopic and elemental analyses were conducted on sediments from piston cores collected from the inner to mid-continental shelf of northern Newfoundland. These data provide a basis to evaluate shifts in the relative contributions of sources of organic matter as a result of changes in productivity or climatological events. Five Units were recognized as representing the sedimentation record from the Late Wisconsinan to present. Unit 5 (the lowermost) consists of glacial till which has average (delta-N-15, delta-C-13 and C/N values of 4.3 parts per thousand, -25.3 parts per thousand and 6.0, respectively. These values suggest that the till was initially deposited in a lacustrine setting prior to subsequent transport and redeposition on the shelf by a Late Wisconsinan ice sheet. The isotopic compositions of Unit 4 indicates a glacial origin with a minor marine influence. The presence of diatom laminations and depletions in C-13 and N-15 in Unit 3 could have resulted from low productivity in cold, nutrient rich waters. A marine origin is assigned to Unit 2, although the variation in isotope values is large: 5.5-9.2 parts per thousand for delta-N-15 and -24.4 to -21.8 parts per thousand for delta-C-13. These shifts are reflective of changes in productivity and the relative contributions of macroalgae and phytoplankton. Holocene sedimentation dominates in Unit 1 and is indicated by deposition of a mixture of phytoplankton and macroalgae.