Climate variability in the North Atlantic Ocean: wind-induced changes in heat content, sea level and overturning.

气候系统被广泛认为是变暖的。据估计，提供给气候系统的大部分额外热量被海洋吸收了。然而，这种海洋变暖并不是一致发生的。对于观测最充分的北大西洋盆地来说，在过去的50年里，热带和中纬度地区一直在变暖，但在高纬度地区却在变冷。热含量的这些变化与风和地表热通量对大气强迫的变化有关。与海洋温度变化一样，盐度也发生了变化，高纬度地区普遍变淡，低纬度地区盐度增加，这可能与大气水循环的加强有关。这些海洋性质的强涡旋尺度对比表明，风强迫和涡旋动力学起着重要作用，这可能反映在倾覆和海平面的动力学信号的变化上。海洋倾覆对这些水团变化的反应似乎令人惊讶：根据我们的历史分析，在过去的50年里，副热带环流略有减弱，亚极环流略有加强。这些倾覆变化可能反映了风强迫的影响，其中回旋尺度的特性变化反馈到倾覆中的变化。风的影响还直接影响到海平面和验潮仪记录的解释：大洋盆地中部的气压年际变化与东部边界海平面之间存在着大范围的相关性。在我们的研究中，我们计划：(1)扩大对北大西洋温度和盐度的历史数据以及超过40年的现有验潮仪记录的分析；(2)进行模式实验，以揭示风变对环流温度和盐度对比的影响、热含量和翻转的关系以及与海平面的关系；以及(3)评估海平面的验潮记录如何受到涡旋动力学和倾覆的影响，这将被用来解释北大西洋海平面上升的长期历史记录的变化。

The climate system is widely accepted as warming. Much of the extra heat provided to the climate system is estimated to have been taken up by the oceans. However, this warming of the oceans is not happening uniformly. For the North Atlantic, the most well observed basin, there has been warming in the tropics and mid latitudes, but cooling at high latitudes over the last 50 years. These changes in heat content are associated with changes in atmospheric forcing from winds and surface heat fluxes. As well as the oceans changing their temperature, there are salinity changes with a general freshening at high latitudes and increase in salinity at low latitudes, perhaps associated with a strengthening in the atmospheric water cycle. The strong gyre-scale contrast in these ocean properties suggest that the wind forcing and gyre dynamics are playing an important role, which are likely to be reflected in changes in the dynamical signals for overturning and sea level. The ocean overturning response to these water-mass changes appears surprising: based on our historical analyses, there is a slightly weakening over the subtropical gyre and slightly strengthening over the subpolar gyre during the last 50 years. These overturning changes might reflect the effect of the wind forcing, where gyre-scale property changes feedback onto changes in the overturning. The effect of the winds also directly affects sea level and the interpretation of the tide gauge record: there are large-scale correlations between the interannual variations in air pressure over the central part of the ocean basins and eastern boundary sea level. In our study, we plan (i) to extend our analyses of the historical data for temperature and salinity over the North Atlantic, as well as the existing tide gauge records longer than 40 years; (ii) conduct model experiments designed to reveal the effect of changing winds on the gyre contrasts in temperature and salinity, on how heat content and overturning are related, and on the relationship with sea level; and (iii) assess how tide gauge records for sea level are affected by gyre dynamics and overturning, which will be used to interpret changes in the long historical records of sea level rise in the North Atlantic.