Spatio-temporal variations of heat stress in coral reef regions over the South China Sea islands from 1985 to 2019
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摘要: 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, NOAA-CRW)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 Niño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。Abstract: 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 Niño. 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 Niño 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 Niño events. The time lag correlation analysis shows that Oceanic Niño 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 7−9 months.
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Key words:
- coral bleaching /
- degree heating weeks /
- heat stress /
- El Niño /
- South China Sea
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图 1 南海诸岛珊瑚礁研究区
南海诸岛珊瑚礁区20 km缓冲(a)和K-means聚类分区(b)的地理空间分布(地图底图来自国家基础地理信息中心,网址:http://www.ngcc.cn/ngcc/)
Fig. 1 Location of coral reef regions in the South China Sea islands
Geographical distribution of 20 km buffer (a) and K-means clustering partition (b) in the coral reef regions of the South China Sea islands
图 3 1985–2019年南海诸岛珊瑚礁区热压力异质性变化
最大周热度(DHW)(a)、年最大DHW趋势(b)、最大DHW年份(c)、年最大DHW ≥ 4℃−周发生的频数(d)、年最大DHW ≥ 8℃−周发生的频数(e)的百分比直方图
Fig. 3 Heat stress heterogeneity changes in the coral reef regions of the South China Sea islands from 1985 to 2019
Percentage histogram of the distribution of maximum degree heating weeks (DHW) (a), annual trend of maximum DHW (b), maximum DHW value in each year (c), frequency of annual maximum DHW ≥ 4℃-weeks (d), frequency of annual maximum DHW ≥ 8℃-weeks (e)
图 5 东沙(a)、西沙(b)、中沙(c)、南沙–1(d)、南沙–2(e)、南沙–3(f)珊瑚礁区月平均周热度(DHW)和ONI的交叉小波能量谱
黑线包围区域内表示其通过5%显著性水平的标准红噪声检验。←表示El Niño与DHW为负位相变化,→表示El Niño与DHW为同位相变化,↓表示El Niño落后DHW变化3个月,↑表示El Niño超前DHW 3个月
Fig. 5 The cross wavelet transform characteristics of monthly mean degree heating week (DHW) of Dongsha (a), Xisha (b), Zhongsha (c), Nansha–1 (d), Nansha–2 (e), and Nansha–3 (f) coral reef area with oceanic Niño index (ONI)
The black lines surrounding areas indicate that it has passed the standard red noise test at the 5% significance level. ← denotes the negative phase change between El Niño and DHW, → denotes the same phase change between El Niño and DHW, ↓ denotes that El Niño lags behind DHW for 3 months, ↓ denotes that El Niño advances DHW for 3 months
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