Study On Spatio-temporal Variation And Influence Factors Of Net Primary Productivity In The Southern Ocean

Since the industrial revolution,global climate change has led to acidification of the oceans and has had a significant influence on the marine ecosystems.As the largest ecosystem in the world,marine ecosystem plays a vital role in global climate control and adjustment.Net primary productivity(NPP)is the most basic parameter of marine ecosystem.It can assess the state of marine ecosystem and truly reflect the productivity of the oceans.The Southern Ocean surrounds the Antarctic continent and connects the Indian Ocean,the Atlantic Ocean and the Pacific Ocean together.As the largest carbon sink over the global ocean,the Southern Ocean absorbs nearly half of the anthropogenic CO2.Climate change has significantly changed the oceanic elements,affecting the absorption of atmospheric CO2 by the Southern Ocean.Therefore,It's of great significance of the study of climate change and the global carbon cycle to investigate the spatio-temporal distribution and recent trend of net primary productivity and the response mechanism to climate factors.Taking the Southern Ocean as the study area,this paper is based on the VGPM-NPP data,sea surface temperature(SST)data,sea ice concentrations(SIC)data,net solar radiation flux(NSRF)data,and the Southern Annular Mode(SAM)index data.Besides,with the help of simple statistical factors,linear trend analysis and simple correlation analysis,the spatial distribution,seasonal variation and recent trend of NPP and climate factors in the Southern Ocean are explored and the influence mechanism of the factors on NPP is revealed.The main conclusion of this paper are as follows:l.The SST of the Southern Ocean with latitude escalating rate is higher.And the range of SST is-1.79? to?6.22?.From?2003?to?2016,there was no significant trend in the average SST of the Southern Ocean.The maximum SST(-0.14?)appeared in the year of?2003?and the minimum SST(-0.27?)appeared in?2015.In general,the SIC of the Southern Ocean with latitude escalating rate is lower,but in some cases,it has regional variability.Because of the existence of polynya around the Antarctic continent,these waters have low SIC.From?2003 to 2016,the area covered by sea ice in the Southern Ocean has a significant rise(6.87×104?km2·a-1,p<0.05).The year of 2004 has the minimum area(9.23×106 km2),and the year of 2014 has the maximum area(1.09×107 km2).In most waters surrounding the Antarctic continent,the SST is significantly decreased and the SIC is significantly increased.In the waters of Bellingshausen sea,the Amundsen Sea,the Ross Sea and the polar front,the SST is significantly increased and the SIC is significantly decreased.2.NPP in the Southern Ocean presents regional variation.For example,NPP around the Antarctic continent and in the Weddell Sea is low,however,the area in the vicinity of the islands shows higher NPP.Meanwhile,high-value also presents near the front of ice shelf,annual average NPP in the study area ranged from 64.0 to 2.26×105 mg C·m-2·a-1,and annual NPP of the Indian Ocean sector,the Atlantic sector and the Pacific sector is 0.568 Gt C·a-1,0.431 Gt C·a-1 and 0.262Gt C·a-1,respectively.3.From 2003 to 2016,the minimum annual sum of NPP of the Southern Ocean appeared in 2008(1.115 Gt C),and the maximum appeared in 2010(1.439 Gt C).Only NPP in the Indian Ocean sector has significantly increased.In terms of spatial distribution,NPP in the waters of the Indian Ocean sector,the eastern part of the Atlantic sector,the northeastern parts of the Weddell Sea and parts of the Pacific Ocean sector have significantly increased,when NPP in the waters of the most parts of the Pacific Ocean sector,part of the Atlantic Ocean sector and near the front of the Amery Ice Shelf decreased significantly.4.Due to the seasonal changes of the solar radiation,NPP in the Southern Ocean has the seasonal variations with the highest value in austral summer and the lowest value in winter.5.By analyzing the factors,like NSRF,SST,SIC and SAM impacted on NPP in the Southern Ocean,we come to:? There was a significant positive correlation between the distribution of NPP and the distribution of SST(R=0.756,p<0.01),and there was a significant negative correlation between the distribution of SIC(R=-0.626,p<0.01).? Seasonal variation of NPP and NSRF has a positive correlation(R=0.951,p<0.01).The main factor limiting NPP in the Southern Ocean from January to June is light,and the factor from July to December is sea ice.? Near the Antarctic continent,the increase of SST and the decrease of SIC will lead to the increase of NPP.In the waters near 60° S,the increase of SST and the decrease of SIC will lead to the decline of NPP.? When SAM is in positive phase,it deepens the depth of the mixed layer in the polar front region,which leads to the decrease of NPP,and it strengthens the upwelling of the waters around 60°S in the Indian Ocean sector,and increases the iron in the sea surface water,resulting in an increase in NPP.? The negative anomaly of SST in the Atlantic sector and at the northern edge of the Pacific Sector in 2007 and 2008 led to a decline in productivity.The negative phase of SAM in 2010 caused a negative anomaly of SIC in Amundsen-Bellingshausen sea,and the positive anomaly of SST at the northern edge of the Atlantic Ocean sector led to an increase in NPP in the year of 2010.