The Mid Pleistocene transition: did marine biological productivity lead to pCO2 changes?"

中更新世转换(MPT)标志着气候从41KYR向100KYR的转变，冰量变化不改变轨道强迫模式。大气中的二氧化碳减少了约30ppm(Wolff等人。2010年，Hönisch等人，2009年)。有孔虫碳同位素在0.9 Ma左右表现出明显的最小值，这是第一个主要的100个KYR旋回出现的时间(Raymo等人，1998)。我们计划检验这一假设是否增强的海洋生物生产力在MPT的气候事件中发挥了作用。已经表明，在陆地干旱增加期间(De Menocal，1995年，Dupont等人，2001年)，高纬度地区沙尘输入的增加(Martinez-Garcia等人，2011年)已导致亚南极南大西洋ODP1090站点的生产力增加。在这里，我们测试全球生产率提高的程度。具体地说，我们问：1)在pCO2atm期间，来自不同气候和水文区域的站点是否伴随着生产力的增加而增加。减少(~0.9 Ma)？2从大陆向海洋输送12C能解释海洋d13C值的降低吗？(与中新世晚期的发现类似(Diester-Haass等人，2006年)。我们(即我的合作伙伴K.Blups(美国)和C.Lear(GB)和我)提出了一种多代理方法来评估MPT期间古生产力的变化及其与冷暖期和底栖有孔虫d13C值的关系。为了估计古生产力，我们将测量底栖有孔虫累积率(BFARs)，并推导出由Herguera(2000)首创并由Diester-Haass等人应用的GC/cm²x Ky值。(2013和这里的参考文献)。我们还将采用一个相对较新的替代指标-浮游有孔虫U/Ca比值作为沉积物氧化还原状态和古生产力的指标(Mawbey和Lear，2013)。我们还将从这些样本中建立底栖有孔虫d13C值的平行记录，以便监测深水中溶解的无机碳的d13C，以评估深水中原位呼吸与有机碳输入的联系程度。海底有孔虫的d18O值将提供与生产力指标相关联的大规模气候变化的记录。这些指标将使我们能够确定出口生产率在这段时间内对气候变化的作用。我们将使用基于文献的信息来增强这些重建，这些信息基于关于陆地输入(特别是作为生产力驱动因素的铁输入)、来自XRF数据(以及Marum-Breme的新测量)和来自古植物学研究(例如，Dupont等人，2001；Schefuçet al.，2005；Clarke et al.，2006)的信息。

The Mid Pleistocene transition (MPT) marks a transition from 41 kyr to 100 kyr cycles in climate and ice volume changes without change in the mode of orbital forcing. Atmospheric pCO2 decreased by about 30 ppm (Wolff et al. 2010, Hönisch et al., 2009). Foraminiferal carbon isotopes display a marked minimum at around 0.9 Ma, the time of emergence of the first major 100 kyr cycles (Raymo et al., 1998).We plan to test the hypothesis whether or not enhanced marine biological productivity played a role in the climatic events of the MPT. It has been shown that enhanced dust input in high latitudes (Martinez-Garcia et al., 2011) during a period of increase in terrestrial aridity (de Menocal, 1995, Dupont et al., 2001) has led to an increase productivity at ODP Site 1090 in the subantarctic South Atlantic. Here we test the global extent of enhanced productivity. Specifically, we ask: 1) Do sites from different climatic and hydrographic regions show concomitant productivity increases during the period of pCO2atm. decrease (~0.9 Ma)? 2) Can transfer of 12C from the continents to the ocean explain the lower marine d13C values? (comparable to findings in the late Miocene (Diester-Haass et al., 2006).We (i.e. my cooperation partners K.Billups (USA) and C. Lear (GB) and I) propose a multiproxy approach to assess changes in paleoproductivity during the MPT and their relation to cold-warm stages and to variations in benthic foraminiferal d13C values. To estimate paleoproductivity, we will measure benthic foraminiferal accumulation rates (BFARs) and derive values in gC/cm² x ky as pioneered by Herguera (2000) and applied by, for example, Diester-Haass et al. (2013 and references herein). We will also employ a relatively new proxy, planktonic foraminiferal U/Ca ratios as an indicator of the sediment redox state of the sediments and paleoproductivity (Mawbey and Lear, 2013). We will also construct parallel records of benthic foraminiferal d13C values from these same samples in order to monitor the d13C of dissolved inorganic carbon of the deep waters, to assess the degree to which the in situ respiration in deep waters can be linked to organic carbon inputs. Benthic foraminiferal d18O values will provide a record of large-scale climate change to which the productivity proxies will be coupled. Together these proxies will allow us to determine the role of export productivity on climate change during this interval of time.We will augment these reconstructions with literature based information about terrestrial input (especially Fe input as a driver of productivity) from XRF data (and new measurements at Marum-Bremen) and from paleobotanical studies (e.g. Dupont et al., 2001; Schefuß et al., 2005; Clarke et al., 2006 ).