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During the last ice age, the Laurentide Ice Sheet exhibited extreme iceberg discharge events that are recorded in North Atlantic sediments1. These Heinrich events have far-reaching climate impacts, including widespread disruptions to hydrological and biogeochemical cycles2–4. They occurred during Heinrich stadials—cold periods with strongly weakened Atlantic overturning circulation5–7. Heinrich-type variability is not distinctive in Greenland water isotope ratios, a well-dated site temperature proxy8, complicating efforts to assess their regional climate impact and phasing against Antarctic climate change. Here we show that Heinrich events have no detectable temperature impact on Greenland and cooling occurs at the onset of several Heinrich stadials, and that both types of Heinrich variability have a distinct imprint on Antarctic climate. Antarctic ice cores show accelerated warming that is synchronous with increases in methane during Heinrich events, suggesting an atmospheric teleconnection9, despite the absence of a Greenland climate signal. Greenland ice-core nitrogen stable isotope ratios, a sensitive temperature proxy, indicate an abrupt cooling of about three degrees Celsius at the onset of Heinrich Stadial 1 (17.8 thousand years before present, where present is defined as 1950). Antarctic warming lags this cooling by 133 ± 93 years, consistent with an oceanic teleconnection. Paradoxically, proximal sites are less affected by Heinrich events than remote sites, suggesting spatially complex event dynamics.

PHOSPHOLIPASE A2(EC 3.1.1.4) catalyses the hydrolysis of the fatty acid ester bond at the 2-position of 1,2 diacyl sn-phosphoglycerides, and has been purified from many sources, such as mammalian pancreas1,2, snake venom3and bee venom4. In mammals, the enzyme is produced as a precursor, which trypsin can convert into active phospholipase A2by splitting the peptide bond Arg 7–Ala 8, with the removal of the N-terminal heptapeptide from the molecule5. The activity of the different phospholipases A2depends on the physical state of the substrate. The enzyme from snake venom is highly active when the substrate is tightly packed in a membrane. Mammalian phospholipases cannot attack membranes; they can degrade the lecithin molecules most effectively when these are more loosely packed in micelles. All phospholipases also have some activity towards substrates in a monomeric solution. The precursors from mammalian pancreas phospholipases are also active towards the monomeric substrate molecules, but inactive to substrates in micellar form6. The primary structure of many of the phospholipases A2is known. They have a single polypeptide chain of approximately 130 amino acid residues and six or seven disulphide bridges7–10. There is a high degree of homology between all the enzymes. We report here the three-dimensional structure of one of these enzymes, prephospholipase A2from porcine pancreas.

Bovine liver rhodanese is a single polypeptide of 293 amino acids in which the halves of the molecule assume analogous tertiary structures in the absence of substantial sequence homology. The sulphur atom transferred during catalysis is bound in persulphide linkage to Cys-247. Substrate binding seems to involve Arg-186 and Lys-249.

The esterolytic enzyme phospholipase A2specifically splits the 2-acyl linkage of phosphoglycerides1in a calcium-dependent reaction. In the pancreas the enzyme occurs as a zymogen which is activated on secretion into the duodenal tract by the removal of seven amino acid residues from the N terminus by trypsin2,3. Having refined our X-ray analysis of the crystal structure of bovine pancreatic phospholipase A2from 2.4 Å (ref. 4) to 1.7 Å resolution5, we now describe how the structure of the molecule may account for the specificity of the enzyme and for the sudden and dramatic change in activity when the substrate concentration passes the critical micelle concentration6.

THE accumulation of vanadium by certain species of tunicates is a case of extremely selective absorption of a rare element from the sea1, where it occurs at its highest valency: as vanadate anion or perhaps vanadyl cation2. In tunicate tissues the chromogen, hsemo-vanadin, is a reducing substance containing trivalent vanadium complexed with sulphate and chelated with the amino groups of protein3. The reducing properties facilitate the detection of vanadium in electron-micrographs of tissues fixed in osmic acid. It has been suggested3that the surfaces of blood cells bind vanadate that has entered the blood plasma without any selective absorption. My evidence pin-points the site of chelation in the blood cells and suggests selective adsorption of vanadyl ions.