Silicate May time-series

Silicate August/September time-series

The macro-nutrients Nitrate, Phosphate and Silicate fuel the growth of the phytoplankton community. Nutrients are replenished into surface waters each year by deep mixing of the water during the stormy winter months.

Cruises each May (upper left) occur around the period when the water column stratifies trapping phytoplankton cells in water with high light and (at least initially) high nutrients. Unlike the other macro-nutrients, silicate is used primarily by the diatom group withtin the phytoplankton for building their siliceous outer skeleton. Diatoms are key components of the spring bloom. Generally nutrients are depleted earlier in warmer years and later in colder years, although there are numerous complications to this simple generalization. The warmer years of 2003-2006 contrast sharply the colder years of 2007-2009.



Cruises in August/September (lower left) show that unlike other macro-nutrients silica is not fully depleted from surface waters, in part because it is replenished from sources besides deep water. Additionally, the diatoms that would use it are less prevalent in surface waters during summer because their growth is more limited by other nutrients. As with other nutrients, the shift of late summer cruises from August to early September starting in 2005 has placed cruises near to the period were surface water temperatures have begun to cool slightly. Stormier weather in September egins to mix surface waters slightly deeper, liberating some deeper nutrients back into surface waters where they may be exploited for a last pulse of phytoplankton growth.

Show patterns for Surface Nitrate & Phosphate