Analysis of longitudinal variations in North Pacific alkalinity to improve predictive algorithms

Abstract

The causes of natural variation in alkalinity in the North Pacific surface ocean need to be
investigated to understand the carbon cycle and to improve predictive algorithms. We used GLODAPv2 to
test hypotheses on the causes of three longitudinal phenomena in Alk*, a tracer of calcium carbonate cycling.
Thesephenomenaare (a)anincreasefromeast to westbetween45°Nand55°N, (b) anincreasefromwest to east
between 25°N and 40°N, and (c) a minor increase from west to east in the equatorial upwelling region. Between
45°N and 55°N, Alk* is higher on the western than on the eastern side, and this is associated with denser
isopycnals with higher Alk* lying at shallower depths. Between 25°N and 40°N, upwelling along the North
American continental shelf causes higher Alk* in the east. Along the equator, a strong east-west trend was not
observed, even though the upwelling on the eastern side of the basin is more intense, because the water
brought to the surface is not high in Alk*. We created two algorithms to predict alkalinity, one for the entire
Pacific Ocean north of 30°S and one for the eastern margin. The Pacific Ocean algorithm is more accurate than
thecommonlyused algorithm publishedby Lee et al. (2006), of similar accuracy to the best previously published
algorithm by Sasse et al. (2013), and is less biased with longitude than other algorithms in the subpolar North
Pacific. Our eastern margin algorithm is more accurate than previously published algorithms.

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Identifiers

ORCID for Toby Tyrrell: orcid.org/0000-0002-1002-1716

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