Collaborative Research: The Great Southern Coccolithophore Belt

知识价值：卫星遥感的最新进展使从空间估计悬浮碳酸钙（颗粒无机碳或“PIC”）成为可能。这种辐射方法在操作上对海洋球石藻（Haptophyceae）具有特异性，并且足够敏感，可以量化少营养环流中的PIC浓度。在MODIS Aqua任务的七年中拍摄的悬浮PIC的全球图像显示，在南大洋亚南极锋面附近有一个环绕地球的PIC“大带”。这一特征每年发生在南方夏季，似乎在南大洋的高营养，低叶绿素区域。大带的面积约为8800万平方公里，占全球海洋的26%。从几次航行到大西洋、印度和太平洋地区的大带地区获得的证据证实了球石藻浓度的升高；先前在大西洋扇区的工作证实了PIC的高光散射。我们仅有的几次船上观测与卫星观测完全一致。在本项目中，研究人员将系统地研究大带的颗石藻，其科学目标如下：(a)确定大带内的颗石藻种类；(b)测量球石藻和相关PIC的丰度；(c)测定球石孔钙化率；(d)阐明可能限制球石团纬度范围的因素（如分层、温度、常量营养素、微量金属、放牧）；(e)证明PIC的可变性是否与出口流量较浅有关；(f)确定PIC产量的变率与二氧化碳分压、总碱度和溶解无机碳收支之间的关系；(g)研究短期海洋酸化对球石藻生长和方解石溶解的影响。这项研究将包括沿南纬50度的巡航，在南方的夏季对大带进行取样。研究人员将结合正在进行的地面采样（主要是光学和水文测量）和垂直站剖面（使用CTD/玫瑰花结和大容量潜水泵）来解决与上述目标相关的假设。巡航轨迹将阐明大带的纬向和经向变化。受控玻璃瓶孵育实验将检验未来不同情景下海洋酸化对球石藻生长和溶解的影响。稀释实验将解决与放牧有关的死亡率和溶解问题。受控的金属添加孵育将侧重于潜在的铁、锌和钴的限制，或与硅藻有关的二氧化硅可用性的竞争。拟议的野外观测和金属添加实验将在全球生物地球化学背景下提供关于大带现状的重要信息。就未来酸化海洋中南大洋球石藻的命运而言，将要进行的海洋酸化实验更具前瞻性。更广泛的影响：大带的全球显著规模表明它可能在全球生物地球化学和气候变化反馈中发挥重要作用。因此，研究人员期望这项工作对生物和化学海洋学产生广泛的、变革性的影响。据预测，燃烧化石燃料造成的海洋酸化将在下个世纪使海洋表面的pH值降低0.3个单位，到2300年将使质子浓度增加5倍。本研究的一个主要目标是在方解石饱和度较低的区域（即，预计方解石饱和度低于饱和的第一个区域之一）检查海洋酸化对球石藻的影响。因此，这些实验的结果将与我们对海洋碳循环的基本认识高度相关。与职业发展和标准II活动相关，该项目包括为来自缅因州大学或学院的NSF REU本科生提供两次巡游的实地体验，为他们参加科学会议提供资金。缅因州大学本科学生的参与为我们这个沿海的乡村州建立了能力，并有助于解决严重的“人才流失”问题，即最优秀的学生离开缅因州，到更富裕、人口更多的州寻找机会。一名教师也将参加巡游（通过nsf赞助的ARMADA计划）。这名教师将为学生开发学习模块，主题包括颗石藻、钙化、出口生产、金属与浮游生物的相互作用、海洋酸化和气候变化。

Intellectual merit: Recent advances in satellite remote sensing enable estimation of suspended calcium carbonate (particulate inorganic carbon or 'PIC') from space. This radiative approach is operationally specific to marine coccolithophores (Haptophyceae) and sensitive enough to quantify PIC concentrations in oligotrophic gyres. Global images of suspended PIC taken over the seven years of the MODIS Aqua mission show a 'Great Belt' of PIC near the sub-Antarctic front of the Southern Ocean that circles the globe. This feature occurs every year during austral summer and appears to be within the high-nutrient, low chlorophyll region of the Southern Ocean. The area of the Great Belt is ~88 million km2, 26% of the global ocean. Evidence from several cruises into the Great Belt region of the Atlantic, Indian and Pacific sectors has verified elevated concentrations of coccolithophores; previous work in the Atlantic sector verified high optical scattering from PIC. The few ship observations we have are entirely consistent with the satellite views. In this project, the investigators will systematically study the coccolithophores of the Great Belt guided by the following science goals: (a) identify the coccolithophore species within this belt; (b) measure the abundance of coccolithophores and associated PIC; (c) measure coccolithopore calcification rates; (d) elucidate factors that may limit coccolithophore latitudinal range (e.g. stratification, temperature, macronutrients, trace metals, grazing); (e) demonstrate whether the variability in PIC relates to shallow export flux; (f) define how variability in PIC production relates to the pCO2, total alkalinity and dissolved inorganic carbon budgets; and (g) examine the impact of short-term ocean acidification on coccolithophore growth and calcite dissolution. The research will involve cruises along the 50 S parallel to sample the Great Belt, during the austral summer. The investigators will use a combination of underway surface sampling (primarily optical and hydrographic) and vertical station profiles (using CTD/rosette and large volume submersible pumps) to address hypotheses related to the above goals. The cruise track will elucidate both zonal and meridional variability in the Great Belt. Controlled carboy incubation experiments will examine the impact of ocean acidification at various future scenarios on coccolithophore growth and dissolution. Dilution experiments will address grazing-related mortality and dissolution questions. Controlled metal-addition incubations will focus on potential iron, zinc and cobalt limitation of the coccolithophores or competition from diatoms related to silica availability. The proposed field observations and metal-addition experiments will provide important information on the current status of the Great Belt in the context of global biogeochemistry. The ocean acidification experiments to be undertaken are more forward-looking in terms of the fate of the Southern Ocean coccolithophores in a future acidified ocean. Broader impacts: The globally significant size of the Great Belt indicates that it likely plays a major role in global biogeochemistry and climate change feedbacks. Thus, the investigators expect this work to have broad, transformative impacts in biological and chemical oceanography. Ocean acidification from the burning of fossil fuels is predicted to lower the pH of the surface ocean by 0.3 units in the next century and up to 0.7 units - a 5-fold increase in the proton concentration by the year 2300. A major goal of this study is to examine the effects of ocean acidification on coccolithophores in a region of low calcite saturation (i.e., one of the first regions expected to become sub-saturating for calcite). The results of these experiments will therefore be highly relevant to our basic understanding of the marine carbon cycle. Related to career development and Criterion II activities, the project includes field experience on two cruises for NSF REU undergraduates from Maine universities or colleges, providing funds for them to attend a scientific meeting. Participation of undergraduate students from Maine colleges builds capacity in our rural coastal state and helps thwart the serious issue of 'brain drain', in which the best students are leaving Maine to seek opportunity in wealthier, more populated states. A teacher will also participate on the cruises (via the NSF-sponsored ARMADA program). This teacher will develop learning modules for students about such topics as coccolithophores, calcification, export production, metal-plankton interactions, ocean acidification and climate change.