Variability of size-fractionated phytoplankton standing stock in the Amundsen Sea during summer

The size-fractionated composition of phytoplankton greatly influences the transfer efficiency of biomass in pelagic food chains and the biological carbon flux from surface waters to the deep sea. To better understand phytoplankton abundance and composition in polynya, ice zone, and open ocean regions of the Amundsen Sea Sector of the Southern Ocean (110°W–150°W), its size-fractionated distribution and vertical structure are reported for January to February 2020. Vertical integrated (0–200 m) chlorophyll (Chl) a concentrations within Amundsen polynya regions are significantly higher than those within ice zone (t test, p 20 μm) contribute 60% of the total Chl in Amundsen polynya and sea ice areas, and form subsurface chlorophyll maxima (SCM) above the pycnocline in the upper water column, probably because of diatom blooms. Net-, nano-, and picoplankton comprise 39%, 32%, and 29% of total Chl in open ocean stations, respectively. The open-ocean SCM migrates deeper and is below the pycnocline. The Amundsen Sea SCM is moderately, positively correlated with the euphotic zone depth and moderately, negatively correlated with column-integrated net- and nanoplankton Chl

Effects of typhoons on surface seawater pCO(2) and air-sea CO2 fluxes in the Northern South China Sea

Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 125(8), (2020): e2020JC016258, doi:10.1029/2020JC016258.This study assessed the effects of typhoons on sea surface pCO2 and CO2 flux in the northern South China Sea (SCS). During the passage of three major typhoons from May to August 2013, sea surface pCO2, surface seawater temperature (SST), and other meteorological parameters were continuously measured on a moored buoy. Surface water in the region was a source of CO2 to the atmosphere with large variations ranging from hours to months. SST was the primary factor controlling the variation of surface pCO2 through most of the time period. Typhoons are seen to impact surface pCO2 in three steps: first by cooling, thus decreasing surface pCO2, and then by causing vertical mixing that brings up deep, high‐CO2 water, and lastly triggering net uptake of CO2 due to the nutrients brought up in this deep water. The typhoons of this study primarily impacted air‐sea CO2 flux via increasing wind speeds. The mean CO2 flux during a typhoon ranged from 3.6 to 5.4 times the pretyphoon mean flux. The magnitude of the CO2 flux during typhoons was strongly inversely correlated with the typhoon center distance. The effect of typhoons accounted for 22% of the total CO2 flux in the study period, during which typhoons occurred only 9% of the time. It was estimated that typhoons enhanced annual CO2 efflux by 23–56% in the northern SCS during the last decade. As such, tropical cyclones may play a large and increasingly important role in controlling CO2 fluxes in a warmer and stormier ocean of the future.This study was supported by the Marine Public Welfare Project of China (Grant 200905012), the Scientific Research Fund of the Second Institute of Oceanography of China (Grant JT1502), the Global Change and Air‐Sea Interaction project of China (Grant GASI‐03‐01‐02‐02), and the National Natural Sciences Foundation of China (Grant 91128212).2021-02-0

Dynamic Gradient Reactivation for Backward Compatible Person Re-identification

We study the backward compatible problem for person re-identification (Re-ID), which aims to constrain the features of an updated new model to be comparable with the existing features from the old model in galleries. Most of the existing works adopt distillation-based methods, which focus on pushing new features to imitate the distribution of the old ones. However, the distillation-based methods are intrinsically sub-optimal since it forces the new feature space to imitate the inferior old feature space. To address this issue, we propose the Ranking-based Backward Compatible Learning (RBCL), which directly optimizes the ranking metric between new features and old features. Different from previous methods, RBCL only pushes the new features to find best-ranking positions in the old feature space instead of strictly alignment, and is in line with the ultimate goal of backward retrieval. However, the sharp sigmoid function used to make the ranking metric differentiable also incurs the gradient vanish issue, therefore stems the ranking refinement during the later period of training. To address this issue, we propose the Dynamic Gradient Reactivation (DGR), which can reactivate the suppressed gradients by adding dynamic computed constant during forward step. To further help targeting the best-ranking positions, we include the Neighbor Context Agents (NCAs) to approximate the entire old feature space during training. Unlike previous works which only test on the in-domain settings, we make the first attempt to introduce the cross-domain settings (including both supervised and unsupervised), which are more meaningful and difficult. The experimental results on all five settings show that the proposed RBCL outperforms previous state-of-the-art methods by large margins under all settings.Comment: Submitted to Pattern Recognition on Dec 06, 2021. Under Revie

On secure NOMA systems with transmit antenna selection schemes

This paper investigates the secrecy performance of a two-user downlink non-orthogonal multiple access systems. Both single-input and single-output and multiple-input and single-output systems with different transmit antenna selection (TAS) strategies are considered. Depending on whether the base station has the global channel state information of both the main and wiretap channels, the exact closed-form expressions for the secrecy outage probability (SOP) with suboptimal antenna selection and optimal antenna selection schemes are obtained and compared with the traditional space-time transmission scheme. To obtain further insights, the asymptotic analysis of the SOP in high average channel power gains regime is presented and it is found that the secrecy diversity order for all the TAS schemes with fixed power allocation is zero. Furthermore, an effective power allocation scheme is proposed to obtain the non-zero diversity order with all the TAS schemes. Monte Carlo simulations are performed to verify the proposed analytical results

Effects of sea ice melt water input on phytoplankton biomass and community structure in the eastern Amundsen Sea

Sea ice melt water and circumpolar deep water (CDW) intrusion have important impacts on the ecosystem of the Amundsen Sea. In this study, samples of nutrients and phytoplankton pigments from nine stations in the eastern Amundsen Sea were collected during the austral summer. Based on in-situ hydrological observations, sea ice density data from satellite remote sensing, and chemical taxonomy calculations, the relationships between environmental factors and phytoplankton biomass and community structure were studied. The results showed that with increasing latitude, the contribution of sea ice melt water (MW%) and the stability of the water body increased, and the depth of the mixed layer (MLD) decreased. The integrated concentration of chlorophyll a (Chl-a) ranged from 21.4 mg·m−2 to 148.4 mg·m−2 (the average value was 35.7±53.4 mg·m−2). Diatoms (diatoms-A [Fragilariopsis spp., Chaetoceros spp., and Proboscia spp.] and diatoms-B [Pseudonitzschia spp.]) and Phaeocystis antarctica were the two most widely distributed phytoplankton groups and contributed 32%±16% and 28%±11%, respectively, of the total biomass. The contributions of Dinoflagellates, Chlorophytes, Cryptophytes, the high-iron group of P. antarctica, and Diatom group A were approximately 17%±8%, 15%±13%, 9%±6%, 5%±9%, and 3%±7%, respectively. The area with the highest phytoplankton biomass was located near the ice-edge region, with a short time lag (Tlag) between sampling and complete sea ice melt and a high MW%, while the area with the second-highest Chl-a concentration was located in the area affected by the upwelling of CDW, with thorough water mixing. Vertically, in the area with a short Tlag and a shallow MLD, the phytoplankton biomass and proportion of diatoms decreased rapidly with increasing water depth. In contrast, in the region with a long Tlag and limited CDW upwelling, the phytoplankton community was dominated by a relatively constant and high proportion of micro phytoplankton, and the phytoplankton biomass was low and relatively stable vertically. Generally, the phytoplankton community structure and biomass in the study area showed high spatial variation and were sensitive to environmental changes

Engineered neutrophil-derived exosome-like vesicles for targeted cancer therapy

Neutrophils are the most abundant innate immune cells in human circulation; however, their derived exosomes have been rarely studied for tumor treatment. Here, we reported that exosomes from neutrophils (N-Ex) induce tumor cell apoptosis by delivering cytotoxic proteins and activating caspase signaling pathway. In addition, we decorated N-Ex with superparamagnetic iron oxide nanoparticles ( SPIONs) to achieve higher tumor-targeting therapeutic effect. We further fabricated exosome-like nanovesicles from neutrophils (NNVs) at high yield. Compared with liposome-loaded doxorubicin (DOX) and natural NNVs, DOX-loaded NNVs show an improved inhibition of tumor cell proliferation. Moreover, DOX-loaded, SPION-decorated NNVs selectively accumulate at the tumor sites under an external magnetic field, effectively restraining tumor growth and extensively prolonging the survival rate in mice. Overall, a simple and effective method to engineer N-Ex and NNVs at clinical applicable scale was developed, which enables the efficient and safe drug delivery for targeted and combined tumor therapy.Peer reviewe

Grazing weakens competitive interactions between active methanotrophs and nitrifiers modulating greenhouse-gas emissions in grassland soils

This work was financially supported by Natural Science Foundation of China (41977033, 41907026, and 41721001), Fundamental Research Funds for the Central Universities (2019QNA6011), National Key Basic Research Program of China (2014CB138801), Shandong Provincial Natural Science Foundation (ZR2019BD032), China Postdoctoral Science Foundation (2020T130387 and 2019M652448). CG-R was funded by a Royal Society University Research Fellowship (UF150571). Special thanks to ChunMei Meng, Yu Luo, and Yan Zheng for their assistance in laboratory analyses.Peer reviewedPublisher PD

Low content of highly reactive iron in sediments from Prydz Bay and the adjacent Southern Ocean: Controlling factors and implications for sedimentary organic carbon preservation

Examining iron (Fe) speciation in marine sediments is critical to understand Fe and carbon biogeochemical cycling in polar regions. In this study, we investigated the speciation of Fe in sediments from Prydz Bay and the adjacent Southern Ocean, and examined the factors controlling Fe speciation and its relationship with total organic carbon (TOC). Our results reveal that unreactive silicate Fe (FeU) is the dominant pool of total Fe (FeT), followed by poorly reactive sheet silicate Fe (FePRS), reducible crystalline Fe oxides (Feox2), easily reducible amorphous/poorly crystalline Fe oxides (Feox1), and magnetite (Femag), with carbonate-associated ferrous Fe (Fecarb) being the smallest pool. The highly reactive Fe (FeHR)/FeT ratios (0.13 ± 0.06) in our study area are among the lowest end-member globally, primarily due to weak bedrock weathering and slow glacier melting. The Feox1/FeT ratios are similar to those in continental shelf and marginal seas containing highly weathered materials, while the Feox2/FeT ratios are significantly lower. This result implicates that low temperature inhibits the aging of iceberg melting-sourced Feox1 potentially, and accordingly the regulation of weathering on the FeHR/FeT ratio is mainly reflected in Feox2/FeT ratio. There are no significant correlations between TOC and FeHR, Fecarb, Feox1 or Feox2 in the research region. Four distinct patterns of TOC/FeHR ratio can be discerned by summarizing the global data set: (a) high TOC/FeHR ratios (> 2.5) are likely the result of high marine primary productivity and low chemically weathered source materials; (b) low TOC/FeHR ratios (< 0.6) are caused by high rates of FeHR inputs and OC remineralization; (c) mid-range TOC/FeHR ratios (0.6 – 2.5) typical of most river particulates and marginal sea sediments indicate the same FeHR and OC sources and/or interactions between each other; (d) both low TOC and FeHR content is the result of low marine primary productivity and weak chemical weathering. Our findings provide new insights into the relationship between FeHR and TOC in polar sediments