Atlantic Coastal Biome
273
Synopsis
Case 2—Nutrient-limited spring production peak, modified by shallow-water processes. The
seasonal production cycle is very well captured by the data used to represent the entire
province (Fig. 9.31). The mixed layer as defined by the pycnocline Z m undergoes strong
austral winter excursion (25 m January, 190 m August) from which it shoals very strongly
in March. Since Z eu lies consistently at 20–40 m, the thermocline is illuminated only very
briefly in austral summer (December–January). The P rate increases linearly from austral
winter minimum to sustained summer maximum, after which the rate declines rapidly to
winter values, this change matching the long winter deepening and brief summer shoaling
(October–March) of Z m over a large depth range (30–225 m). Significant near-surface
chlorophyll occurs at all seasons, and whereas the period of significant accumulation in
austral winter (June–July) is largely coastal, that of summer (November–February) is also
offshore, especially at the shelf break. These observations are consistent with only an
approximate production-consumption balance year-round.