The seasonal cycle at station ALOHA in OFES and in the observations

Note: the data from OFES are only from year 2004 so far.

• Chlorophyll (chl) is maximum near 100-125 m depth in the observations while it is maximum at the surface in the OFES model (Figs. 1 and 3). The 1/3-deg. model of Oschlies et al. (2000; their Fig. 9) and 1/9-deg. model of Oschlies (2002b; his Fig. 5b failed also to reproduce the subsurface maximum of chl at the BATS station. Notice that the subsurface maximum is statistically significant as his mean value of about 0.25 is about 4 to 5 times larger than its standard deviation (not shown).
• The seasonal cycle of density seems, however, relatively well reproduced (Figs. 1 and 3) with shallowing of the isopycnal at the end of winter, a deepening with a surface warm layer in spring and summer followed by the first mixing event in fall.

Figure 1: Seasonal chlorophyll at station ALOHA using data from May 2000 to May 2007. The dashed lines are isopycnals from the seasonal cycle of potential density computed using data from January 2000 to December 2008 (computed with RESEARCH/PROJECTS/MARINE_BIOLOGY/SUBMESOSCALE_PROCESSES/Station_ALOHA/seasonal_cycle.m)

Figure 2: Seasonal intrate at station ALOHA. The dashed lines are isopycnals from the seasonal cycle of potential density. All data are from January 2000 to December 2008 (computed with RESEARCH/PROJECTS/MARINE_BIOLOGY/SUBMESOSCALE_PROCESSES/Station_ALOHA/seasonal_cycle.m)

• The basic structure of nitrate is also well represented, without surprise. I do not think we can say much about the variability in depth of the contours given that the mean values obtained for each month are only about twice as large as their corresponding standard deviation (not shown).
• Notice, however, the intrusion of nitrate into lighter isopycnal layers in OFES (Fig. 4, especially between the contours of potential density of 25.4 and 25.8 kg/m^3). Could this be related to the same events in the float observations (in OFES, diapycnal anomalies of nitrate are in the order of 0.5-1 mmol N/m^3, which corresponds to 7-14 mg/mol, a value consistent with the float observations)? What causes these intrusions? Could we guess them using eSQG theory?

Figure 3: Chlorophyll near station ALOHA in OFES during 2004. White contours are isopycnals for the same year (computed with RESEARCH/PROJECTS/MARINE_BIOLOGY/SUBMESOSCALE_PROCESSES/OFES/annual_cycle_ALOHA_BATS_OFES_obs.m).

Figure 4: Nitrate near station ALOHA in OFES during 2004. White contours are isopycnals for the same year (computed with RESEARCH/PROJECTS/MARINE_BIOLOGY/SUBMESOSCALE_PROCESSES/OFES/annual_cycle_ALOHA_BATS_OFES_obs.m).