Abstract Saltmarsh evolution is closely linked to sea-level rise (SLR) and sediment supply. In a regime of accelerating SLR, saltmarsh survival depends on the ability of the marsh platform to grow vertically through organic and inorganic accumulation, and laterally via transgression over adjacent uplands. In formerly glaciated settings, the formation and maintenance of a saltmarsh are complicated by steep uplands, low sediment availability, isostatic rebound, changes to tidal amplitudes, and anthropogenic alteration. While much work has examined the development of large saltmarshes in New England since the mid-Holocene and Anthropocene, little is known about the smaller isolated saltmarshes that form in pockets along the glaciated coastline. We use radiocarbon dates from newly uncovered index points (basal peat) within Boston Harbor to date one of the oldest saltmarshes in the region (∼4.2 ka), and calculate the polynomial relative sea-level curve (RSLR) for the lower Gulf of Maine taking into account tidal amplification throughout the Holocene. This study informs the historical persistence of isolated saltmarshes under varying rates of sea-level rise (magnitude as much as 2 mm yr−1). Additionally, we refine the timing and rates of the mid-Holocene sea-level deceleration in this region: between 2.8 and 3.3 ka, slowing from 2.1 mm yr−1 to 0.5 mm yr−1. RSLR determined from the past century of tide gauge data is 2.86 mm yr−1, five times greater than historic rates over the past 2000 years. Recent vertical accretion rates (determined from marker horizons and 210Pb data) indicate that portions of Boston Harbor’s saltmarshes are able to keep pace with current RSLR. However, historical diking and ditching practices appear to have resulted in elevation loss and conversion from high saltmarsh platforms to low saltmarsh platforms, largely influencing the amount of inorganic sediment needed to help maintain marsh surfaces. These results highlight that knowledge of historical anthropogenic modifications and changes in hydroperiod are critical when interpreting vertical accretion results. More importantly, anthropogenic modification within sediment starved saltmarshes may be the cause for cannibalization of marsh shorelines, whereby inorganic sediment eroded from marsh edges is recycled and delivered to the surface, facilitating vertical accretion that offsets RSLR. Under modern accelerated sea-level rise and decreased sediment supply, this cannibalization process may now be the only pathway for saltmarsh survival.

中文翻译：

---

波士顿港全新世盐沼的可持续性：缅因湾下游的新海平面曲线以及近期人为改变的影响

摘要 盐沼演化与海平面上升（SLR）和沉积物供应密切相关。在加速 SLR 的情况下，盐沼的生存取决于沼泽平台通过有机和无机积累垂直生长的能力，以及通过邻近高地的海侵而横向生长的能力。在以前的冰川环境中，陡峭的高地、低沉积物可用性、均衡反弹、潮汐幅度变化和人为改变使盐沼的形成和维护变得复杂。虽然许多工作已经研究了自全新世中期和人类世以来新英格兰大型盐沼的发展，但对沿着冰川海岸线形成的较小的孤立盐沼知之甚少。我们使用来自波士顿港内新发现的索引点（基底泥炭）的放射性碳日期来确定该地区最古老的盐沼之一（~4.2 ka），并计算缅因湾下游的多项式相对海平面曲线（RSLR）考虑到整个全新世的潮汐放大。这项研究揭示了孤立盐沼在不同海平面上升速率（幅度高达 2 mm yr-1）下的历史持久性。此外，我们改进了该地区全新世中期海平面减速的时间和速率：在 2.8 和 3.3 ka 之间，从 2.1 mm yr-1 减慢到 0.5 mm yr-1。从过去一个世纪的潮汐测量数据确定的 RSLR 为 2.86 mm yr−1，是过去 2000 年历史速率的五倍。最近的垂直吸积率（根据标记层和 210Pb 数据确定）表明波士顿港的盐沼部分能够与当前的 RSLR 保持同步。然而，历史上的堤防和开沟做法似乎导致了海拔下降和从高盐沼平台到低盐沼平台的转变，在很大程度上影响了帮助维持沼泽表面所需的无机沉积物的数量。这些结果强调，在解释垂直吸积结果时，历史人为修改和水周期变化的知识至关重要。更重要的是，沉积物匮乏的盐沼中的人为改造可能是沼泽海岸线自相残杀的原因，从沼泽边缘侵蚀的无机沉积物被回收并输送到地表，促进抵消 RSLR 的垂直吸积。在现代海平面加速上升和沉积物供应减少的情况下，这种蚕食过程现在可能是盐沼生存的唯一途径。