it, the Liebigian nutrient.
(^) Upper-water-column SRP data from the HOT site
(http://hahana.soest.hawaii.edu/hot/hot-dogs/interface.html) (Fig. 11.29) show wide
and somewhat chaotic variations. The series to 2009 shows that supply and drawdown
are intermittent without any obvious periodicity. Phosphate mixes upward with
substantial intermittency. Periods of higher levels may result from greater winter
mixing, and short-lived up-ticks at HOT may be generated by passing cyclonic eddies.
Johnson et al. (2010), using an Argo float equipped with oxygen and nitrate sensors,
demonstrated that there is such intermittent delivery of nutrients to the euphotic zone.
It was launched at HOT, moved mostly east between 22° and 24°N, and profiled from
1000 m to the surface every 5 days for 127 cycles (21 months). There were 12
substantial upward mixing events identified from increased nitrate, particularly in the
upper nutricline, and subsequent oxygen increase showed that substantial
photosynthesis resulted. Possibly some events were missed between profiles, because
of the extreme rapidity of nitrate uptake when it does appear. Intermittency of upward
nutrient mixing is consonant with cyclonic eddies being the primary mechanism.
Fig. 11.29 Time-series of soluble reactive phosphate (SRP) at Station ALOHA. From
data available as “upper water column SRP” from the HOT web site
(http://hahana.soest.hawaii.edu/hot/hot-dogs/interface.html.).
Nitrogen Fixation
(^) Subtropical gyres and equatorial zones are the sites of biological nitrogen fixation, the
conversion of dissolved gaseous N 2 to ammonium and amine compounds. The general
topic is well reviewed by Carpenter and Capone (2008) and covered here in Chapter