Circum-Antarctic age modelling of Quaternary marine cores under the Antarctic Circumpolar Current: ice-core dust-magnetic correlation

Sediments in the belt under the Antarctic Circumpolar Current (ACC) contain high quantities of siliceous microfossils (mainly diatoms) and very little to zero carbonate. This prevents establishment of the age by the usual methods of oxygen isotope stratigraphy at most coring sites. Downcore variation in magnetic susceptibility (MS) from cores from the Scotia Sea closely resembles the temporal pattern of dust concentration and flux in East Antarctic ice cores. The validity of the temporal correlation between marine MS and EPICA Dome C (EDC) dust on the EDC3 time scale is established through C-14 dating of the acid insoluble organic matter back to 30 ka, and radiolarian abundance stratigraphy of Cycladophora davisiana back to 180 ka. The correlations are good (r>0.80) and give credence to the use of MS-dust as a means of establishing chronostratigraphy in carbonate-free pelagic sediments from the Southern Ocean. This correlation has been established in >10 cores in the Scotia Sea. The circum-Antarctic validity of the pattern is shown in correlations to MS in sediment cores from the Indian and SW Pacific sectors of the Southern Ocean. During MIS 3 (57-29 ka), when sedimentation rates at correlated core sites exceeded 10 cm ka(-1). three MS maxima in the marine sediments and dust peaks at EDC, respectively, correspond to the cool periods between Antarctic warm events A1-A4. We have not established the precise cause of the correlation. but its validity around the circum-Antarctic west wind belt suggests that the material was either all transported by wind or was supplemented by wind-driven current transport. The fact that it occurs also in sections with a low terrigenous content suggests a fine grained, high-susceptibility material such as magnetite as the likely source. (C) 2009 Elsevier B.V. All rights reserved

Estudo das estruturas cristalinas de argilominerais provenientes de depósitos auríveros resultantes de alterações hidrotermais

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Supplementary Material for: Hypomagnesemia in Hemodialysis Patients: Role of Proton Pump Inhibitors

<b><i>Background:</i></b> Recent observations have associated hypomagnesemia with increased risk of cardiovascular morbidity and mortality in hemodialysis patients. <b><i>Methods:</i></b> We did a 3-month chart review of 62 chronic hemodialysis patients at a single US hospital. All were dialyzed using a dialysate [Mg] of 0.75-1.0 mEq/l. Patients were divided into two groups: hypomagnesemic (mean predialysis plasma [Mg] <1.5 mEq/l) and non-hypomagnesemic (mean predialysis plasma [Mg] ≥1.5 mEq/l). <b><i>Results:</i></b> All patients were male; mean age was 64.3 ± 8.7 years and the majority (73%) diabetic. 24 patients (39%) had hypomagnesemia and 38 (61%) were not hypomagnesemic. There were no significant differences between the two groups in age, diabetes status, blood pressure, duration of dialysis, plasma calcium, phosphorus, albumin, intact parathyroid hormone (PTH), dialysis adequacy (Kt/V), or dietary protein intake (as estimated by normalized protein catabolic rate, nPCR). However, use of proton pump inhibitors (PPIs) was significantly associated with hypomagnesemia (plasma [Mg] 1.48 ± 0.16 mEq/l in the PPI group vs. 1.65 ± 0.26 mEq/l in the non-PPI group, p = 0.007). Adjustment for age, diabetes status, duration of dialysis, plasma albumin, Kt/V, nPCR, and diuretic use did not affect the association between PPI use and hypomagnesemia. <b><i>Conclusions:</i></b> Use of PPIs in patients dialyzed using a dialysate [Mg] of 0.75-1.0 mEq/l is associated with hypomagnesemia. We suggest monitoring plasma [Mg] in patients taking PPIs, with discontinuation of the medication if possible and/or adjustment of dialysate [Mg] to normalize plasma [Mg]