Societal importance of Antarctic negative feedbacks on climate change: blue carbon gains from sea ice, ice shelf and glacier losses.

Diminishing prospects for environmental preservation under climate change are intensifying efforts to boost capture, storage and sequestration (long-term burial) of carbon. However, as Earth's biological carbon sinks also shrink, remediation has become a key part of the narrative for terrestrial ecosystems. In contrast, blue carbon on polar continental shelves have stronger pathways to sequestration and have increased with climate-forced marine ice losses-becoming the largest known natural negative feedback on climate change. Here we explore the size and complex dynamics of blue carbon gains with spatiotemporal changes in sea ice (60-100 MtCyear-1), ice shelves (4-40 MtCyear-1 = giant iceberg generation) and glacier retreat (< 1 MtCyear-1). Estimates suggest that, amongst these, reduced duration of seasonal sea ice is most important. Decreasing sea ice extent drives longer (not necessarily larger biomass) smaller cell-sized phytoplankton blooms, increasing growth of many primary consumers and benthic carbon storage-where sequestration chances are maximal. However, sea ice losses also create positive feedbacks in shallow waters through increased iceberg movement and scouring of benthos. Unlike loss of sea ice, which enhances existing sinks, ice shelf losses generate brand new carbon sinks both where giant icebergs were, and in their wake. These also generate small positive feedbacks from scouring, minimised by repeat scouring at biodiversity hotspots. Blue carbon change from glacier retreat has been least well quantified, and although emerging fjords are small areas, they have high storage-sequestration conversion efficiencies, whilst blue carbon in polar waters faces many diverse and complex stressors. The identity of these are known (e.g. fishing, warming, ocean acidification, non-indigenous species and plastic pollution) but not their magnitude of impact. In order to mediate multiple stressors, research should focus on wider verification of blue carbon gains, projecting future change, and the broader environmental and economic benefits to safeguard blue carbon ecosystems through law.

A andomized contraceptive trial comparing a daily progestogen with a combined oral contraceptive steroid.

PIP: This study was designed as a double-blind trial of .25 mg ethynodiol diacetate versus the combined, established preparation, Ovulen 21 (1 mg ethynodiol diacetate and .1 mg mestranol). Blanks were added to the sets of Ovulen 21 capsules so that there was no obvious difference in appearance of the medications. 43 young women enrolled in each group. There were more dropouts in the experimental group so that the average number of months of study was 9.2 for the control group and only 6.7 for the experimental group. The experimental group reported more intercyclic bleeding and more irregularity of cycles than the Ovulen 21 control group (p.001 in each case). Cramping was reported 3 times more frequently by the experimental group, (p.05). There was 1 unusually prolonged case of amenorrhea (7 months) in a patient taking ethynodiol diacetate. This patient responded to discontinuation of the tablet and had a menstrual cycle within 36 days. There were no unintended pregnancies.^ieng