Circumpolar Projections of Antarctic krill (Euphausia superba) growth potential

These data represent the results of the first study to use Earth System Model (ESM) outputs of SST and chlorophyll-a to simulate circumpolar krill growth potential for the recent past (1960-1989) and future climate change scenarios (2070-2099). Growth potential is obtained using an empirically-derived krill growth model (Atkinson et al. 2006, Limnol. Oceanogr.), where growth is modeled as a function of SST and chlorophyll-a. It serves as an approximation of habitat quality, as areas that support high growth rates are assumed to be good habitat (see Murphy et al., 2017, Sci Rep).

To increase confidence in the future projections, ESMs were selected and weighted for each season based on their skill at reproducing observation-based krill growth potential for the recent past. First, eleven ESMs which provided SST and chlorophyll-a outputs were obtained from the Coupled Model Inter-comparison Project 5 archive. These included: CanESM2, CMCC-CESM, CNRM-CM5, GFL-ESM2G, GFDL-ESM2M, GISS-E2-H-CC, HadGEM2-CC, IPSL-CM5A-LR, MPI-ESM-MR, MRI-ESM1 and NorESM1-ME. For each ESM, seasonal surface averages of SST and chlorophyll-a were used to calculate growth potential for the historical scenario (1960-1989), which was then bilinearly interpolated on to the same 1°x1° grid. Satellite observation-based datasets for SST and chlorophyll-a were used to calculate observation-based growth potential for the recent past (1997-2010). These comprised seasonal surface averages of SST (from the OISST v2 daily dataset, 1/4⁰ horizontal resolution) and chlorophyll-a (the mean of the SeaWiFS and Johnson et al. (2013) corrected estimate of SeaWiFS daily datasets, 1/12⁰ horizontal resolution). Observation-based growth potential was then bilinearly interpolated onto the same grid as the ESMs.

ESM skill for each season was subsequently assessed against observation-based growth potential using a Taylor Diagram. The ESMs were selected and weighted according to their performance to produce a weighted subset (see "ESM_weighting_method.pdf" file). Of the netcdfs provided, "hist_mean_ensemble.nc" represents the unweighted mean of seasonal growth potential, calculated from the initial ensemble of eleven ESMs for the historical scenario. The "hist_mean_subset.nc" file represents the analogous output of the weighted subset.

Future projections of seasonal growth potential for Representative Concentration Pathways (RCPs) 4.5 and 8.5 were obtained using the weighted subset for the period of 2070-2099. These projected seasonal surface averages are provided in the "rcp45_mean_subset.nc" and "rcp85_mean_subset.nc" files. RCPs represent standard climate change scenarios developed by the Intergovernmental Panel on Climate Change, with 4.5 reflecting some mitigation of carbon emissions, and 8.5 being the "business as usual" scenario.

Analogous netcdfs for the weighted subset outputs of chlorophyll-a (chl) and SST (tos) for the historical and RCP scenarios are also provided in the "chl_tos_netcdfs.zip" file so that the driving environmental variables underlying growth potential can be examined.

本数据集为首个利用海表温度（Sea Surface Temperature, SST）与叶绿素a的地球系统模式（Earth System Model, ESM）输出结果，模拟近期（1960-1989年）与未来气候变化情景下（2070-2099年）环极磷虾生长潜力的研究成果。本研究采用经验推导的磷虾生长模型（Atkinson等，2006，《Limnology and Oceanography》）计算生长潜力，该模型将生长速率建模为SST与叶绿素a的函数。由于生长速率较高的区域被视为优质栖息地，因此生长潜力可近似表征栖息地质量（详见Murphy等，2017，《Scientific Reports》）。

为提升未来情景预测的可信度，本研究基于各地球系统模式对基于观测的磷虾生长潜力的重现能力，按季节筛选并加权各ESM。首先从耦合模式比较计划第五阶段（Coupled Model Inter-comparison Project 5, CMIP5）的存档中获取11套可输出SST与叶绿素a数据的ESM，分别为：CanESM2、CMCC-CESM、CNRM-CM5、GFL-ESM2G、GFDL-ESM2M、GISS-E2-H-CC、HadGEM2-CC、IPSL-CM5A-LR、MPI-ESM-MR、MRI-ESM1及NorESM1-ME。针对每套ESM，利用其季节平均海表参数计算历史情景（1960-1989年）下的磷虾生长潜力，随后将结果双线性插值至统一的1°×1°网格。同时采用卫星观测数据集，计算近期（1997-2010年）的基于观测的磷虾生长潜力：其中SST数据来自OISST v2逐日数据集（水平分辨率1/4°），叶绿素a数据为SeaWiFS逐日数据集与Johnson等（2013）修正后的SeaWiFS逐日数据集的均值（水平分辨率1/12°）。最终将基于观测的生长潜力同样双线性插值至与ESM结果一致的网格。

随后，针对每个季节，利用泰勒图（Taylor Diagram）将各ESM的模拟结果与基于观测的生长潜力对比，评估其模拟性能。本研究依据各ESM的表现筛选并加权，得到加权子集（详见"ESM_weighting_method.pdf"文件）。在本次提供的NetCDF文件中，"hist_mean_ensemble.nc"为11套初始ESM在历史情景下的季节生长潜力的未加权均值；"hist_mean_subset.nc"则为加权子集的对应输出结果。

利用该加权子集，本研究计算了典型浓度路径（Representative Concentration Pathways, RCPs）4.5与8.5情景下2070-2099年的季节生长潜力预测结果，相关数据分别存储于"rcp45_mean_subset.nc"与"rcp85_mean_subset.nc"文件中。RCPs为政府间气候变化专门委员会开发的标准气候变化情景，其中RCP4.5代表实施了一定碳排放减缓措施的情景，RCP8.5则为“一切照常”的基准情景。

本次还在"chl_tos_netcdfs.zip"压缩包中提供了历史情景与RCP情景下，加权子集输出的叶绿素a（chl）与SST（tos）数据的对应NetCDF文件，以便研究者分析支撑磷虾生长潜力的关键环境驱动变量。