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Which was the habitat of early Eocene planktic foraminifer Chiloguembelina? Stable isotope paleobiology from the Atlantic Ocean and implication for paleoceanographic reconstructions
Global and Planetary Change ( IF 3.9 ) Pub Date : 2020-08-01 , DOI: 10.1016/j.gloplacha.2020.103216
Valeria Luciani , Roberta D'Onofrio , Giulia Filippi , Simone Moretti

Abstract The planktic foraminiferal genus Chiloguembelina is characterized by tiny test and biserial disposition of chambers. Largely accepted ecological interpretation ascribes biserial planktic foraminifera as eutrophic and low-oxygen tolerant forms inhabiting the Oxygen Minimum Zone (OMZ). However, this ecological interpretation does not agree with all available data from Cenozoic record. Actually, chiloguembelinid stable isotope paleobiology is highly variable through time and space as it indicates mixed-layer habitat on earliest Eocene, middle Eocene and Late Oligocene but thermocline habitat during middle Eocene from northwest Atlantic Ocean. However, chiloguembelinid stable-isotope data were so far lacking from the early Eocene. This interval includes the early Eocene Climatic Optimum (EECO, ~53–48 Ma) that is the crucial time when Earth's surface temperatures and pCO2 reached their maximum levels in the Cenozoic. We present here new chiloguembelinid oxygen and carbon stable-isotope data from early Eocene Atlantic Ocean Drilling Program (ODP) Sites 1051, 1258, 1263 and 690. We also generate new data on Chiloguembelina abundance from Site 1051 and compare our record with those previously published from sites 1263 and 1258 in order to correlate the early Eocene paleoceanographic distribution of this genus through the Atlantic Ocean. Interestingly, Chiloguembelina became virtually absent at the beginning of the EECO in the subtropical, equatorial and temperate Atlantic sites. Our findings clearly prove that early Eocene Chiloguembelina occupied a deep-water niche throughout the Atlantic Ocean as demonstrated by its stable isotope signature close to the deep-dweller Subbotina and benthic foraminifera. These evidences provide critical paleoceanographic implications suggesting that intermediate water temperatures probably rose significantly during the EECO thus becoming too warm for this genus. Elevated ocean temperatures enhanced the rate of bacterial respiration and remineralization significantly thus resulting in more efficient recycling of nutrients higher in the water column. This would have induced a restricted food supply deeper in the thermocline and cut out the chiloguembelinid niche. The agreement of the observed decline in abundance of chiloguembelinids at the study sites with recently published foraminifera-bound nitrogen isotope data suggests that enhanced oxygenation of the thermocline in the early EECO might have also played a major role in driving the disappearance of chiloguembelinids, which in itself represent a new evidence for the largely accepted view that these forms inhabited the OMZ. Very likely a combination of reduced food supply, increase in thermocline temperature and oxygen content resulted in the decline of chiloguembelinids in the early EECO.

中文翻译:

哪个是始新世早期浮游有孔虫 Chiloguembelina 的栖息地?来自大西洋的稳定同位素古生物学及其对古海洋学重建的意义

摘要 浮游有孔虫属 Chilogueembelina 的特点是细小,室壁呈双列排列。被广泛接受的生态解释将双列浮游有孔虫归咎于富营养化和低氧耐受形式,栖息在最低氧区 (OMZ)。然而,这种生态解释与新生代记录中的所有可用数据不一致。实际上,chiloguembelinid 稳定同位素古生物学在时间和空间上具有高度可变性,因为它表明最早的始新世、中始新世和晚渐新世的混合层栖息地,但西北大西洋中始新世的温跃层栖息地。然而,迄今为止,尚缺乏始新世早期的 chiloguembelinid 稳定同位素数据。该区间包括始新世早期气候最适 (EECO, ~53–48 Ma),这是地球表面温度和 pCO2 在新生代达到最大值的关键时间。我们在此展示了来自始新世早期大西洋钻探计划 (ODP) 站点 1051、1258、1263 和 690 的新的 chiloguembelinid 氧和碳稳定同位素数据。我们还生成了来自站点 1051 的 Chiloguembelina 丰度的新数据,并将我们的记录与之前发表的数据进行了比较来自站点 1263 和 1258,以便关联该属在大西洋中的早期始新世古海洋学分布。有趣的是,在亚热带、赤道和温带大西洋地区的 EECO 开始时,Chiloguembelina 几乎不存在。我们的研究结果清楚地证明,早期始新世 Chiloguembelina 占据了整个大西洋的深水生态位,正如其靠近深居生物 Subbotina 和底栖有孔虫的稳定同位素特征所证明的那样。这些证据提供了重要的古海洋学意义,表明在 EECO 期间中间水温可能显着上升,因此对于该属而言变得过于温暖。海洋温度升高显着提高了细菌呼吸和再矿化的速度,从而使水体中较高的营养物质更有效地循环利用。这会导致温跃层更深处的食物供应受到限制,并切断 chiloguembelinid 生态位。在研究地点观察到的 chiloguembelinids 丰度下降与最近发表的与有孔虫结合的氮同位素数据的一致性表明,早期 EECO 中温跃层的增强氧化也可能在推动 chiloguembelinids 消失方面发挥了重要作用,其中其本身代表了一个新的证据,即这些形式居住在 OMZ 中的广泛接受的观点。很可能由于食物供应减少、温跃层温度升高和含氧量增加,导致早期 EECO 中chiloguembelinids 的数量下降。这本身就代表了一个新的证据,证明了这些形式居住在 OMZ 中的普遍接受的观点。很可能由于食物供应减少、温跃层温度升高和含氧量增加,导致早期 EECO 中chiloguembelinids 的数量下降。这本身就代表了一个新的证据,证明了这些形式居住在 OMZ 中的普遍接受的观点。很可能由于食物供应减少、温跃层温度升高和含氧量增加,导致早期 EECO 中chiloguembelinids 的数量下降。
更新日期:2020-08-01
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