Dynamical suppression of sea level rise along the Pacific coast of North America: Indications for imminent acceleration

Abstract

[1] Long-term changes in global mean sea level (MSL) rise have important practical implications for shoreline and beach erosion, coastal wetlands inundation, storm surge flooding, and coastal development. Altimetry since 1993 indicates that global MSL rise has increased about 50% above the 20th century rise rate, from 2 to 3 mm yr −1 . At the same time, both tide gauge measurements and altimetry indicate virtually no increase along the Pacific coast of North America during the satellite epoch. Here we show that the dynamical steric response of North Pacific eastern boundary ocean circulation to a dramatic change in wind stress curl, t xy , which occurred after the mid-1970s regime shift, can account for the suppression of regional sea level rise along this coast since 1980. Alarmingly, mean t xy over the North Pacific recently reached levels not observed since before the mid-1970s regime shift. This change in wind stress patterns may be foreshadowing a Pacific Decadal Oscillation regime shift, causing an associated persistent change in basin-scale t xy that may result in a concomitant resumption of sea level rise along the U.S. West Coast to global or even higher rates.

Spatial Patterns of Sea Level Variability Associated with Natural Internal Climate Modes

“…Along the same line of arguments, regression From Behera and Yamagata (2010) analyses indeed show that PDO-and NPGO-related wind stress curl and alongshore wind ( Fig. 6) can cause decadal sea level variations in the ocean interior and along the coasts by inducing Rossby waves (e.g., Qiu 2002), coastal Kelvin waves (e.g., Clarke and Lebedev 1997;Thompson et al 2014), upwelling, andhorizontal advection (Di Lorenzo et al 2008;Bromirski et al 2011). Hamlington et al (2014) extracted the basin-wide surface winds associated with the PDO by regressing surface winds available from the European Centre for Medium-Range Weather Forecasts (ECMWF) operational ocean analysis/reanalysis system (ORA-S3) (Balmaseda et al 2008) onto sea level PC1 from 1950 to 2010.…”

“…Modeling studies suggest that warming of the tropical Indian and Atlantic Oceans enhances surface easterly trade winds and thus contributes to the intensified SLR (e.g., Luo et al 2012;Han et al 2014a;Hamlington et al 2014;England et al 2014;McGregor et al 2014); however, a large portion of this rapid SLR-together with weak falls in the eastern basin-is part of the basin-scale sea level pattern associated with the Pacific Decadal Oscillation (PDO) or decadal variability of ENSO (Bromirski et al 2011;Merrifield et al 2012;Meyssignac et al 2012;Zhang and Church 2012;Hamlington et al 2013Hamlington et al , 2014Moon et al 2013;Han et al 2014a; Palanisamy et al 2015). The PDO is defined as the leading empirical orthogonal function (EOF) of sea surface temperature (SST) anomaly over the North Pacific ([20°N), and the leading principal component (PC1) is referred to as the PDO index (e.g., Mantua et al 1997;Minobe 1997;Zhang et al 1997;Garreaud and Battisti 1999; see review papers by Alexander 2010;Liu 2012).…”

“…Regionally, they are similar to the North Pacific EOF1 of the upper 500 m thermosteric sea level from 1950 to 1998 (Lombard et al 2005) and tropical Pacific EOF1 of reconstructed sea level from 1950 to 2009 . Many studies have shown that decadal sea level variability in different regions of the Pacific including the marginal seas and US west coast is significantly correlated with the PDO index (e.g., Bromirski et al 2011;Merrifield 2011;Marcos et al 2012;Zhang and Church 2012).…”

“…Independently, Bromirski et al (2011) also examined the effects of surface wind and heat flux using OGCM experiments, showing that local wind stress curl dominates heat flux in causing decadal sea level variability along the US west coast. suggested the dominance of remote equatorial wind stress, rather than the local wind stress curl, in driving decadal sea level variability along the US west coast during recent decades.…”

Sea level trends in Southeast Asian seas

“…In some regions, internal climate variability on decadal (or longer) timescales can lead to trends that are significantly larger than the background secular trend. Identifying and explaining signals contributing to regional and global sea level variability and trends has been a frequently studied problem in recent years (e.g., Bromirski et al, 2011;Chambers et al, 2012;Hamlington et al, 2011aHamlington et al, , 2013Hamlington et al, , 2014bMerrifield et al, 2012;Zhang and Church, 2012;Fasullo et al, 2013;Moon et al, 2013;Frankcombe et al, 2014).…”