"O2 declines and the shoaling of the hypoxic boundary in the CA current" paper summary

[TeresaGonz]

• Overview

  • discusses a "shoaling effect" of the oxygen minimum layer due to global warming that causes stratification of the water column

• stratification does not allow oxygen from the upper layers to fall to deeper depths which brings up the OML (oxygen min layer)
• "observations point to a basin-wide reduction in DO."

• Method

  • "We computed linear trends of DO at six standard levels (50, 100, 200, 300, 400 and 500 m) at each station over the period 1984–2006, and determined the correlation coefficient and significance value of each fit. A linear trend was considered significant for p-values less than 0.05. Trends were computed for all 66 nominal stations, with the average number of occupations ranging from 93 (500 m) to 98 (50 m). From the linear fit, we determined the magnitude of the oxygen trend at each standard depth and station, as well as the percent change over the 23-year period. We did not consider surface oxygen trends, as these are impacted by high-frequency air-sea fluxes and can vary widely [Garcia et al., 2005]."

• Identified Hypoxic Zones

  • largest DO declines in upper 100 m @ center of line 77
  • largest decline at 50 m at Station 87.40
  • "significant DO declines at mid-depths (52 stations at 200 m, 47 at 300 m), with the largest declines (-1.8 mmol/kg/y) on the offshore end of Lines 90 and 93."
  • "the hypoxic boundary has shoaled by up to 90 m (at station 93.30). The shoaling of this layer is significant at 37 of 46 stations"

[mgupta701]

It might be interesting to run regression on the data from the stations cited, at the standard levels (50, 100, 200, 300, 400 and 500 m) and see if we can also identify significant negative relationship between oxygen and time.

I will start working on doing this for 50 m at Station 87.40

[TeresaGonz]

"CalCOFI samples the upper portion of the oxygen minimum layer (OML) in the southern California Current [Kamykowski and Zentara, 1990], thus the observed water column DO declines can be interpreted as a shoaling of the OML. In particular, the level of the OML representing an accepted threshold for hypoxia (􏰁 60 mmol/kg; Diaz and Rosenberg [1995]) has shoaled by an average of 41 m since 1984 (Figure 4). Within the inner SCB and near Point Conception, the hypoxic boundary has shoaled by up to 90 m (at station 93.30). The shoaling of this layer is significant at 37 of 46 stations"