On the integrity of a commercial cassette ultrafiltration membrane: implications for marine colloidal biogeochemistry

The performance and integrity of a cassette cross-flow ultrafilter （Pellicon 2, Millipore） are examined with a suite of macromolecules of different molecular masses. The retention coefficient during the cross-flow ultrafiltration experiments increases with increasing molecular mass and reaches 90% with 10 kDa dextran in both milli-Q water and ultrafiltered seawater media. Based on a 90% retention coefficient, the molecular mass cut-off for the ultrafiltration membrane is defined at 10 kDa, which is ten times （1 kDa） that rated by the manufacturer. To further validate the accuracy of the laboratory calibration, the samples from the lower Zhujiang River and the Jiulong River Estuary are ultrafiltered with the cassette ultrafiltration membrane and the colloidal organic carbon abundances in these samples are quantified with the ultrafiltration per- meation model based on time series permeation subsamples. The colloidal organic carbon abundances are 5.8%-21.1% in the Jiulong River Estuary and 5.6%-11.0% in the lower Zhujiang River. These are consistent with the reported values for both estuaries as well as with the colloidal organic carbon abundances in ma- rine environments over the coastal and open oceans with 10 kDa cut-off membranes. Therefore, these field data support the laboratory calibration result and indicate the validity of the experimental and quantification procedure adopted. The discrepancy between the nominal molecular mass cut-off and the actual pore size of the ultrafiltration membrane should be of great concern for research in colloidal and nanoparticle biogeochemistry. Careflfl examination of the membrane integrity should be taken during ultrafiltration ex- oeriments in order to avoid misleading molecular mass cut-off information.

Impacts of ocean acidification under multiple stressors on typical organisms and ecological processes

The oceans are taking up over one million tons of fossil CO_(2) per hour,resulting in increased/ρCO_(2) and declining pH,leading to ocean acidification(OA).At the same time,accumulation of CO_(2) and other greenhouse gases is causing ocean warming,which enhances stratification with thinned upper mixed layers,exposing planktonic organisms to increasing levels of daytime integrated UV radiation.Ocean warming also reduces dissolved oxygen in seawater,resulting in ocean deoxygenation.All these ocean global changes are impacting marine ecosystems and effects are well documented for each individual driver(pH,oxygen,temperature,UV).However,combined effects are still poorly understood,strongly limiting our ability to project impacts at regional or local levels.Different regions are often exposed(and often adapted)to contrastingly different physical and chemical environmental conditions and organisms,and ecosystems from different parts of the world will be exposed to unique combinations of stressors in the future.Understanding the modulating role of adaptation,species niche and stressors’interaction is key.This review,being a non-exhaustively explored one.aims to provide an overview on understandings of ecophysiological effects of OA and its combination with covarying drivers,mainly warming,deoxygenation and solar UV radiation.We propose a testable hypothetical model as well as future research perspectives.

后新冠疫情时代的气候变化

An unprecedented global crisis of COVID-19 pandemic evokes the world’s thinking about the future of humankind. This pandemic is no doubt one of the major disasters in human history, comparable to the medieval Black Death(bubonic plague), and the 1918 influenza. It is even called the ‘‘Third World War" because of the profound impacts on the political, economic and global order.Doomed as historical event。