1985–2019年南海诸岛珊瑚礁区热压力时空变化研究分析

Spatio-temporal variations of heat stress in coral reef regions over the South China Sea islands from 1985 to 2019

全球气候变暖引起的热压力增大是南海诸岛珊瑚礁面临的最主要威胁,基于热压力对珊瑚礁白化的评估有利于对其保护和管理。周热度(Degree Heating Week,DHW)可以衡量热压力的强度和持续时间,代表过去连续12周珊瑚礁区海表温度(SST)正异常的累积。本文基于美国国家海洋和大气管理珊瑚礁监测计划(National Oceanic and Atmospheric Administration-Coral Reef Watch,NOAACRW)海表温度数据集,逐像元对35个年最大周热度数值进行K-means聚类分析,将南海诸岛珊瑚礁区分为6个区域:南沙–1、南沙–2、南沙–3、东沙、西沙和中沙珊瑚礁区。分析南海诸岛珊瑚礁区1985–2019年热压力时空变化及其与El Ni?o的相关关系。结果表明:(1)南海诸岛珊瑚礁区最大DHW为0~12.9℃-周,纬度上由高到低呈现减小变化规律。(2)线性拟合法分析1985–2019年的年最大DHW,显示南海诸岛珊瑚礁区热压力强度呈现上升趋势,为0.013~0.174℃-周/a,南海诸岛珊瑚礁区最大DHW出现在1998年、2010年、2014年。(3)年最大DHW可能造成93.9%的珊瑚礁发生超过一次白化的风险,19.6%的珊瑚礁发生超过一次死亡的风险。(4)南海诸岛珊瑚礁区的月均DHW和ONI交叉小波分析显示两者存在多时段8~32个月共振周期的时频特征和时滞相关性,证实南海诸岛珊瑚礁热压力随着厄尔尼诺事件发生而显著增大;时滞相关分析表明,ONI与南海诸岛珊瑚礁区热压力呈正相关关系,后者滞后于前者7~9个月的时间。

Increasing heat stress due to global warming is the main threat to coral reef regions over the South China Sea islands. Coral reefs bleaching events are most often predicted by heat stress, which will benefit the protection and management coral reefs. Degree heating week(DHW) is used to measure the intensity and duration of heat stress experienced on coral reefs, represents the accumulation of positive sea surface temperature(SST) anomaly at that location over the past 12 week periods. This study utilizes the National Oceanic and Atmospheric Administration-Coral Reef Watch(NOAA-CRW) SST dataset to investigate spatio-temporal in the heat stress of the coral reef regions of the South China Sea islands between 1985 to 2019 and its relevance to El Ni?o. K-means cluster analysis was performed on the 35-year maximum degree heating week values per pixel, and the coral reefs of the South China Sea islands were divided into 6 regions: Nansha-1, Nansha-2, Nansha-3, Dongsha, Xisha and Zhongsha coral reef region. The main results are as following:(1) The maximum DHW of the coral reef regions of the South China Sea islands is 0-12.9°C-week, and it decreases from high to low in latitude.(2) The linear fitting method was used to analyze the annual maximum DHW from 1985 to 2019. The results showed that the thermal pressure intensity in the coral reef area of the South China Sea islands showed an upward trend, ranging from 0.013°C to 0.174°C per week. The maximum DHW in the coral reef area of the South China Sea islands appeared in 1998, 2010, 2014.(3) The maximum annual DHW might have caused 93.9% of coral reefs to have more than one bleaching risk event,and 19.6% of coral reefs to have at least one risk of death.(4) The cross-wavelet analysis of monthly mean DHW in the coral reef regions of the South China Sea islands and Oceanic Ni?o index shows that there are time-frequency characteristics and time-lag correlation of multi-period 8-32 months resonance period, which confirms that the thermal pressure of coral reefs in the South China Sea islands increases significantly with the occurrence of El Ni?o events. The time lag correlation analysis shows that Oceanic Ni?o index is positively correlated with the thermal pressure in the coral reef regions of the South China Sea islands, and the latter lags behind the former by 7-9months.