Classification of seamount morphology and its evaluating significance of ferromanganese crust in the central Pacific Ocean

Using the SeaBeam technology, the morphology of seamount and its relation to the formation of cobalt-rich crust in the central Pacific Ocean were surveyed during the cruise in 2003 for marine mineral resources. The result shows that seamounts can be divided morphologically into the spire seamount and the fiat topped seamount. These two types of seamount bear great differences in their landform, lithology and cobalt-rich crust. On the upper portion of the fiat topped seamount, the fiat top and the sharp escarpments are unfavorable to the growth of crust, and, consequently, the crusts here are mostly laminar or gravelly, their thicknesses generally show great variations, and the consecutive ore body often develops in its deep water region. On the spire topped seamount, however, the fiat area is small, and its gradient is constant without large variation from the top to the bottom. This favors the growth of cobalt-rich crust and often leads to consecutive tabular ore body of medium thickness, occurring on the spire topped seamount from the shallow water region to the deep water region. The cobalt-rich crust on the spire topped seamount is much better than that on the fiat topped seamount for the crust abundance, crust coverage and number of ore-occurrences within unit area. Furthermore, the crust on the spire topped seamount is rich in cobalt, nickel, manganese elements of high economic value. Because the crust with high quality ore often occurs in the shallow water region on the spire topped seamount, it can be mined and use more easily in the future.

Estimation of Age,Growth and Maturation of Purpleback Flying Squid,Sthenoteuthis oualaniensis,in Bashi Channel,Central Pacific Ocean

The age, growth and maturation of Sthenoteuthis oualaniensis were determined with statolith data collected with a light purse seine from the Bashi Channel of central Pacific Ocean. The estimated longevity of the squid was no more than 6 months for females, and no more than 5 months for males. Growth in mantle length(ML) was best described by logistic models for both females and males, while growth in body weight(BW) was best fitted by power curves. The maximum absolute growth rate(AGR) and instantaneous growth rate(IGR) in ML or BW both occurred at 91–105 days for females and 76–90 days for males. Back calculated hatching dates were from October to January, with a peak in December, although the short duration of sampling date might have had an influence on the result. The lower percentage of mature females(37.2%) suggested that the study area during the sampling date was not a spawning ground for the species. Size and age at first maturity were 183 mm ML and 136 days for females, whereas they were 156 mm ML and 85 days for males.

Modeling a habitat suitability index for the eastern fall cohort of Ommastrephes bartramii in the central North Pacific Ocean

The eastern fall cohort of the neon flying squid, Ommastrephes bartramii, has been commercially exploited by the Chinese squid jigging fleet in the central North Pacific Ocean since the late 1990s. To understand and identify their optimal habitat, we have developed a habitat suitability index （HSI） model using two potential important environmental variables -- sea surface temperature （SST） and sea surface height anomaly （SSHA） -- and fishery data from the main fishing ground （165°-180°E） during June and July of 1999-2003. A geometric mean model （GMM）, minimum model （MM） and arithmetic weighted model （AWM） with different weights were compared and the best HSI model was selected using Akaike＇s information criterion （AIC）. The performance of the developed HSI model was evaluated using fishery data for 2004. This study suggests that the highest catch per unit effort （CPUE） and fishing effort are closely related to SST and SSHA. The best SST- and SSHA-based suitability index （SI） regression models were SISST-based = 0.7SIeffort-SST ＋ 0.3 SICPUE-SST, and SISSHA-based =0.5Sleffort-SSHA ＋ 0.5SICPUE-SSHA, respectively, showing that fishing effort is more important than CPUE in the estimation of SI. The best HSI model was the AWM, defined as HSI=0.3SISSHA-based＋ 0.7SISSHA-based, indicating that SSHA is more important than SST in estimating the HSI of squid. In 2004, monthly HSI values greater than 0.6 coincided with the distribution of productive fishing ground and high CPUE in June and July, suggesting that the models perform well. The proposed model provides an important tool in our efforts to develop forecasting capacity of squid spatial dynamics.

Impacts of the SSTs over Equatorial Central–Eastern Pacific and Southeastern Indian Ocean on the Cold and Rainy/Snowy/Icy Weather in Southern China

Low temperature together with snow/freezing rain is disastrous in winter over southern China.Previous studies suggest that this is related to the sea surface temperature(SST)anomalies,especially La Nina conditions,over the equatorial central–eastern Pacific Ocean(EP).In reality,however,La Nina episodes are not always accompanied by rainy/snowy/icy(CRSI)days in southern China,such as the case in winter 2020/2021.Is there any other factor that works jointly with the EP SST to affect the winter CRSI weather in southern China?To address this question,CRSI days are defined and calculated based on station observation data,and the related SST anomalies and atmospheric circulations are examined based on the Hadley Centre SST data and the NCEP/NCAR reanalysis data for winters of1978/1979–2017/2018.The results indicate that the CRSI weather with more CRSI days is featured with both decreased temperature and increased winter precipitation over southern China.The SSTs over both the EP and the southeastern Indian Ocean(SIO)are closely related to the CRSI days in southern China with correlation coefficients of-0.29 and 0.39,significant at the 90%and 95%confidence levels,respectively.The SST over EP affects significantly air temperature,as revealed by previous studies,with cooler EP closely related to the deepened East Asian trough,which benefits stronger East Asian winter monsoon(EAWM)and lower air temperature in southern China.Nevertheless,this paper discovers that the SST over SIO affects precipitation of southern China,with a correlation coefficient of 0.42,significant at the 99%confidence level,with warmer SIO correlated with deepened southern branch trough(SBT)and strengthened western North Pacific anomalous anticyclone(WNPAC),favoring more water vapor convergence and enhanced precipitation in southern China.Given presence of La Ni?a in both winters,compared to the winter of 2020/2021,the winter of 2021/2022 witnessed more CRSI days,perhaps due to the warmer SIO.