Mechanism study of the 2010–2016 rapid rise of the Caribbean Sea Level

https://doi.org/10.1016/j.gloplacha.2020.103219Get rights and content

Highlights

  • There was a significant rise in the Caribbean Sea level during 2010–2016.

  • The thermo- and halo- steric expansion contributed 5.34 cm to this sea level rise.

  • Lateral exchanges also contributed to the rise and changed vertical water structure.

  • Change in Atlantic inflow is larger than Gulf of Mexico return flow to the basin.

  • The sea level change mechanism shows a local moderation of Stefan-Boltzmann law.

Abstract

The Caribbean Sea level increased rapidly by about 6.55 cm in the period 2010–2016. This dramatic rise occurred concurrently with a step change in basin mass (freshwater equivalent) of about 1.09 cm (relative to 2006–2009) and an increase in surface freshwater loss of about 5.96 cm. Using re-analysis and satellite-derived atmosphere and ocean physics datasets, we investigate the driver for this episode of sea level rise and its impact on vertical water structure. Our conclusion is that increase in Caribbean sea evaporation, which removes latent heat and cools surface waters, caused upward longwave radiation to decrease, resulting in warming and total steric sea level rise of about 5.34 cm; and saline water that compensated for increased surface freshwater loss caused basin mass to increase due to the additional salt. Because of these concurrent changes, surface layer and mixed layer salinity and temperature increased; and adjustments of the Atlantic inflow and Gulf of Mexico return flow (equivalent net lateral exchange increase of about 7.05 cm) deepened the interface between the stratified top water and bottom rest water of the Caribbean Sea. This study highlights the useful role of the Caribbean Sea for illustrating local mechanisms and patterns of sea level variability in a changing global climate.

Introduction

This paper aims to explain the 2010–2016 rapid rise of the Caribbean Sea level. Sea level rise is of vital importance to the well-being of many population centers around the Caribbean Sea (Fig. 1) and the sensitive marine ecosystem there (Severance and Karl, 2006; Chollett et al., 2012; Fish et al., 2015; Carrilo et al., 2017; Heidarzadeh et al., 2018). Because of the high rate of occurrence of hurricane events in the Caribbean Sea, sea level rise increases the risk of storm surges in coastal regions (Montoya et al., 2018). The Caribbean Sea level rise will also increase coastal flooding, and salinization of coastal wetlands and aquifers (Jury, 2018). However, despite these consequences of sea level rise, there are no basinwide records of Caribbean Sea observations, and relatively few observation-based studies that examine trends in the Caribbean Sea level (Chollett et al., 2012; Montoya et al., 2018).

The Caribbean Sea, a semi-enclosed sea located in the Northern Hemisphere tropics between the Atlantic and Pacific Ocean, is an evaporative basin because evaporation there exceeds precipitation and runoff (Beier et al., 2017). Seasonal and interannual variability in the Caribbean Sea atmospheric and oceanographic conditions are large (Corredor and Morell, 2001; Angeles et al., 2010; Dunion, 2011; Ruiz-Ochoa et al., 2012; Jury, 2018; Rueda-Roa et al., 2018). Sea level, SST and evaporation in the Caribbean Sea increase from April to September (warming season) and decrease from October to March (cooling season) (Durán-Quesada et al., 2010; Ruiz-Ochoa et al., 2012).

Two subsystems of the North Atlantic, the Gulf Stream and the Gulf of Mexico, are associated with the Caribbean Sea, which makes this sea a vital indicator of global change. The Atlantic inflow enters the Caribbean Sea at the eastern boundary and exits through the Yucatan Strait where this flow bifurcates: one branch flows through the Florida Strait and reconnects with the North Atlantic Western Boundary Current, and the other branch forms a loop current within the Gulf of Mexico (Murphy et al., 1999; Fratatoni, 2001; Johns et al., 2002; Centurioni and Niiler, 2003; Cetina et al., 2006; Rousset and Beal, 2011; Athié et al., 2012). To compensate the Atlantic inflow, there is a bottom Gulf of Mexico return flow to the Caribbean Sea (Bunge et al., 2002; Sheinbaum, 2002; Abascal, 2003; Chérubin, 2005; Lin et al., 2009; Pérez-Santos et al., 2010; Sturges, 2013; van Westen et al., 2018). The circulation structure within the Caribbean Sea is characterized by eddies of diverse length scales throughout the whole domain (Murphy et al., 1999; Andrade and Barton, 2000; Ezer et al., 2005; Richardson, 2005; Lin et al., 2011; Jouanno et al., 2012; Hughes et al., 2016), which promotes mixing (Sheng and Tang, 2003).

During the period 2010–2016, the Caribbean Sea level increased by about 6.55 cm. To explain this event, we strive to answer two questions: 1) what is the driver for this episode of sea level rise? and 2) what are the impacts of this sea level rise on the Caribbean Sea vertical structure? In this same period, sea level decreased in the Atlantic inflow region (trend is −0.12 cm/yr and correlation coefficient with Caribbean Sea level is 0.06) and increased in the Gulf of Mexico region near the Yucatan Strait (trend is 1.9 cm/yr and correlation coefficient with Caribbean Sea level is 0.46). These two boundary trends are very likely also to influence Caribbean Sea level, therefore we analyzed the characteristics of the upstream and downstream lateral exchanges. Moreover, the Caribbean Sea level trend is different from these two boundary trends, indicating the importance of factors local to this sea. The rest of this paper is structured as follows: in section 2 we examine the causes of the Caribbean Sea level rise and present our hypothesis for this event; in section 3 we analyze the space and time variability of the Caribbean Sea level; in section 4 we show the effects of sea level rise on Caribbean Sea vertical structure; and section 5 is summary and conclusion.

Section snippets

Causes of the Caribbean Sea level rise

We used satellite-derived SSALTO/DUACS sea level anomaly (SLA), which has 0.25o resolution (Pujol et al., 2016; Copernicus, 2019a), to analyze the Caribbean Sea level trend. Beginning in 2004, there was an upward trend in basin-average sea level, with a rapid rise in the period 2010–2016 (Fig. 2a). For this 7-year period, annual sea level rise is about 0.94 (the 95% confidence interval is between 0.79 and 1.09) cm/yr. We hereafter focus on this episode (i.e. 2010–2016) of rapid sea level rise.

Horizontal structure

Because our hypothesis is derived using basin-average variables, we first evaluated the appropriateness of basin-averaging by analyzing the horizontal structure of the Caribbean Sea level. We employed empirical orthogonal function (EOF) analysis for the 26-year (1993–2018) monthly SLA in order to distinguish sea level horizontal characteristics within the Caribbean Sea. The dominant mode (Mode 1) accounts for 99.1% of temporal-horizontal structure, and the second largest mode accounts for only

Effects of Sea Level rise on Caribbean Sea vertical structure

Using this four-layer vertical structure, we then examined the basin-average temperature and salinity time series for each layer (Fig. 5). The upward (warming) trend in the basin-average temperature during the period 2010–2016 is evident (Fig. 5a): this trend is highest in layer 1, followed by layer 2, and smallest in layer 3; but there is no warming trend in layer 4 temperature. There is also an upward trend in basin-average salinity (Fig. 5b): the highest salinity increase is in layer 1,

Summary and conclusion

The Caribbean Sea level increased rapidly during the period 2010–2016. We used satellite-derived and reanalysis atmosphere and ocean physics datasets to demonstrate that this sea level rise episode is the combined effect of upward trends in total steric expansion and mass change. Considering the water exchanges at the eastern and western boundaries of the Caribbean Sea, our hypothesis to explain these concurrent upward trends is that increase in Caribbean Sea evaporation, which removes latent

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Data availability

All datasets used for this study can be obtained from the indicated citations.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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