Siliceous microplankton fluxes and seasonal variations in the central South China Sea during 1993–1995: monsoon climate and El Niño responses

Seasonal variations of radiolarian and diatom fluxes in the central South China Sea during 1993–1995 were overwhelmingly controlled by monsoon climate. Radiolarian and diatom increased obviously during the Northeast (from November to February) and Southwest (from June to September) monsoons and decreased during the periods between the monsoons. The change of circulation driven by the monsoons improved water exchange in the different areas that brought rich nutrient materials for the surface microplankton, thereby enhancing radiolarian and diatom fluxes. Variation of radiolarian flux coincided with organic carbon flux, surface primary and export productivities. High radiolarian flux corresponded to high surface primary productivity. Radiolarian and diatom fluxes raised abnormally during 1994–1995 could be attributed to the El Nino event during the period.     

Premonitory phenomenon of El Ni(n)o event reflected in the observations of LOD and sea level

Data sets of the changes of the length of day, the sea surface temperature in the eastern Pacific and of the sea level in Hong Long from tide gauge observations are used to analyze and reveal the reflections in the observations of the length of day and the sea level changes concerned with the premonitory phenomenon of next El Ni(n)o event. The results from this study indicate that a new El Ni(n)o event has been brewing with the ending of the strong La Nina event that started in early summer of 1998. The estimated formation period of the new El Ni(n)o event will begin before the end of 2000, and the peak period may be reached at around the end of 2001.     

Connection between interannual variability of the western Pacific and eastern Indian Oceans in the 1997 - 1998 El Nino event

In this paper, the sea surface height and the heat content of the upper ocean are analyzed to retrieve the relationship of interannual variabilities between the tropical western Pacific and eastern Indian Oceans during the 1997 - 1998 El Nino event. In the prophase of this El Nino, the negative sea level anomalies (SLA) occurred in the tropical western Pacific (TWP) firstly, and then appeared in the tropical eastern Indian Ocean (TEI). The negative heat content anomalies (HCA) emerged in the TWP before this El Nino burst while the SLA signals developed over there. During the mature stage of this El Nino, two kinds of signals in the TWP and TEI turned to be the maximum negative sequently. Due to the connected interannual adjustment between the TEI and TWP, we adopted a method to estimate the Indonesian Throughflow (ITF) transport by calculating the HCA budget in the TEI. The indirect estimation of the ITF was comparable to the observation values. Therefore, the anomalies in the TEI had been proved as adv     

Twenty-five years of change in scleractinian coral communities of Daya Bay （northern South China Sea） and its response to the 2008 AD extreme cold climate event

Coral reefs worldwide are becoming increasingly and detrimentally impacted upon by a variety of factors including significant climate changes, such as global warming and increased El Nino-Southern Oscillation activity. Generally, the persistence of coral reefs, especially at low-latitudes, is governed, in part, by sea surface temperatures not exceeding the critical limit （-30℃） at which mass mortality can occur. Thus, it is thought that corals living at high-latitudes （i.e., currently cooler sea surface temperatures） will likely respond more favourably to hypothesized future temperature increases than corals living at low-latitudes （i.e., currently warmer sea surface temperatures）. Consequently, high-latitude coral communities may have the potential to act as regions of refugia for many coral species in the face of potential future global warming. The Daya Bay （22°31′--22°50′N）, northern South China Sea, contains several high-latitude non-reefal coral communities and represents one of the most northerly distributions of scleractinian corals within the region. Significantly, Daya Bay has experienced dramatic warming in both air and sea surface temperatures throughout the past 50 years. In this paper, we analyze 25 years of change in the Daya Bay coral communities, based both on historic surveys and our latest 2006--2008 regional ecological surveys. Our results suggest that, contrary to predictions, there have been significant declines in coral cover within the Daya Bay during the past 25 years （i.e., 76.6% coral cover in 1983/1984 to only 15.3% coral cover by 2008）. Such changes also reflect a significant shift in the most abundant coral species, from Acropora pruinosa to Favites abdita. Most of the modern coral communities became established between 15 and 30 years ago, corresponding to a period of increased winter sea surface temperature. However, very few colonies have become established within the last 15 years, despite a more intense period of warming. By taking into account additional factors, we hypothesize that direct anthropogenic impacts, rather than climatic events, have both restricted the development, and drove the decline, of Daya Bay coral communities in the last 15 years. The Daya Bay has also been subjected to occasional extreme cold events during the past 50 years, with the most recent occurring in early 2008 （13 January-13 February）. During the 2008 cold event, the lowest air temperature reaches only 6.6℃, and the mean sea surface temperature for February fall to 〈 14℃, including six continuous days at 12.3℃. Significantly, the sea surface temperatures fall below the hypothesized critical lower temperature threshold （-13℃） that commonly leads to mass mortality in scleractinian coral communities. Surprisingly, our coral community surveys, conducted both before （August 2007） and after （late February 2008） the extreme 2008 cold event, demonstrate that the Daya Bay coral ecosystems are barely impacted upon during the cold period. Those observations suggest that the Daya Bay scleractinian coral communities have developed adaptations to low sea surface temperatures. Overall, our data support the hypothesis that high-latitude coral communities, such as Daya Bay, have the potential to act as areas of refugia for scleractinian corals in the advent of potential future global warming.