Potential influence of the Deepwater Horizon oil spill on phytoplankton primary productivity in the northern Gulf of Mexico

Yao Li,Chuanmin Hu,Huilin Gao,Antonietta Quigg

doi:10.1088/1748-9326/ab3735

Abstract

Nine years after the Deepwater Horizon (DwH) oil spill (20 April–15 July 2010), the recovery of primary productivity at the ocean surface remains to be investigated. Here, we used the normalized fluorescence line height (nFLH) from the Moderate Resolution Imaging Spectroradiometer as an indicator of chlorophyll a concentration (Chl a). First, from the spatiotemporal variations of nFLH between 2001 and 2017, a reduction of nFLH after the DwH oil spill was observed (for a relatively long period, from 2011 to 2014). Second, a stepwise multiple regression model was used to examine which of the following environmental factors could explain the annual variations in nFLH: river discharge, total nitrogen load, total phosphorus load, photosynthetically available radiation, sea surface temperature and wind speed. Results show that river discharge, sea surface temperature and wind speed are the primary factors that regulated the annual nFLH variations in the DwH area during the pre-spill years. In contrast, this same model could not explain the reduction of nFLH for the four years after the DwH oil spill. After 2015, nFLH appears to have resumed to the pre-spill concentrations. Here we suggest that the nFLH reduction between 2011 and 2014 could have originated from the DwH oil spill, although the exact mechanism is yet to be determined.

Highlights

The Deepwater Horizon (DwH)6 oil spill, which occurred between 20 April, 2010 and 15 July, 2010, released over 130 million gallons of crude oil over the course of 87 d into the Gulf of Mexico
From the monthly mean time series, it is evident that the normalized fluorescence line height (nFLH) had seasonal patterns with peaks of 0.151–0.227 mW cm−2 μm−1 sr−1 during the winter (December–February) and dips of 0.062–0.095 mW cm−2 μm−1 sr−1 in the late spring to early summer (May to July)
Based on the stepwise multiple regression analysis of the anomaly data, Q, sea surface temperature (SST), and wind speed (WS) were identified as the most significant factors regulating the anomaly of chlorophyll a (Chl a) in the DwH area

Summary

Introduction

The Deepwater Horizon (DwH) oil spill, which occurred between 20 April, 2010 and 15 July, 2010, released over 130 million gallons of crude oil over the course of 87 d into the Gulf of Mexico. It is the largest marine oil spill in US history (Crone and Tolstoy 2010, McNutt et al 2012). Girard and Fisher (2018) demonstrated—using high-definition imagery data— that deep-sea corals were heavily impacted and had not recovered by 2017. As for the food web, the oil spill may have led to a significant decrease of the fishery yield which could take more than 30 years (especially for some slowly-growing populations) to recover fully (Ainsworth et al 2018). Long term studies are required—especially given the long life cycles of many of the organisms of interest, and the interannual variability in the meteorological and environmental conditions of the Gulf of Mexico

Objectives

Methods

Results

Discussion

Conclusion