古老森林的遗迹在海底深处被发现，距离陆地数千英里，科学家在孟加拉湾底部的沉积层中发现了1900万年前的木片。
洛杉矶南加州大学的萨拉·费金斯领导的研究人员从海面下钻了两英里多，从海底下半英里处取回沉积物。通过分析核心样本，该团队能够观察到几百万年前树木是如何被卷进海洋，然后被困在地下的。
通过观察核心的木片，团队能够确定这些树来自哪里。在大多数情况下，他们发现木材来自海洋附近低地的树木。然而，其中一层被发现有来自喜马拉雅山的树木的木材，这些树木生长在海拔大约两英里的地方。
在他们的研究中，发表于PNAS该小组认为，一片古老森林中的树木是由于大量的水释放而被连根拔起的——这可能是由冰川或滑坡形成的天然水坝造成的。科学家们建议，这些树木在被释放到孟加拉风扇之前，会沿着汹涌的水流被运送数千英里——来自旋风、季风或洪水。
该小组说，这是第一个证据表明树木可以被运输数千英里，从山脉到深海。他们的发现也揭示了木材在地球碳循环——碳从大气层进入地球及其有机体，然后又返回的方式。
储存在植物中的碳在被食用、腐烂或燃烧时会释放出来。因为树木在被连根拔起后不久就被运走了——死亡点——它们没有腐烂。取而代之的是，新鲜木材被锁在海底沉积物中——这可能代表了一种以前未被认识到的碳可以储存数百万年的方法。
研究人员写道:“跨越1900万年在浊积岩粗颗粒层中发现的木质碎片]表明，木质输入可能是孟加拉扇和其他大陆边缘地质时间尺度上[有机碳循环中被忽视的一个贡献者。”他们补充说，这些发现表明，锁定在大陆边缘的有机碳可能比以前认为的要高。他们说:“木材的快速出口和掩埋代表了大气二氧化碳封存的高效途径。”。
费尔金斯说，了解森林被冲入海洋后会封存多少碳对于了解未来的气候变化非常重要。她在一份声明中说:“当我们试图计算碳循环各个部分的碳含量时，我们并不知道这片埋藏在海底的树木碎片森林。”。"现在我们需要把它加入等式中."
科学家们目前正在努力理解碳循环，美国的研究人员发起了深层碳观测站(DCO)十多年前。该组织最近发布的一份报告显示，地球总碳不到1%位于地表之上——海洋、陆地和大气中。其余的都被锁在地球的地壳、地幔和地核里。
展示孟加拉湾的股票照片。研究人员在海面下两英里处钻孔，寻找古树被冲到数千英里外的证据。
TREES FROM ANCIENT FORESTS DISCOVERED IN DEEP OCEAN, THOUSANDS OF MILES FROM LAND
The remains of ancient forests have been discovered deep beneath the sea, thousands of miles from land, with scientists finding 19 million-year-old wood chips in sediment layers at the bottom of the Bay of Bengal.
Researchers led by Sarah Feakins, from the University of Southern California, Los Angeles, drilled down over two miles from the surface of the ocean, retrieving sediments from half a mile beneath the sea floor. By analyzing the core sample, the team was able to look at how trees were swept into the ocean millions of years ago before getting trapped in the ground.
By looking at the wood chips in the core, the team was able to determine where the trees had come from. In most cases, they found the wood was from trees that grew in lowlands, near the ocean. However, one layer was found to have wood from trees that would have grown high in the Himalayan mountains, about two miles above sea level.
In their study, published in PNAS, the team argues that trees within an ancient forest were uprooted by a huge release of water—potentially by a natural dam created by a glacier or a landslide. These trees would have then been transported for thousands of miles along a huge surge of water—from cyclones, monsoons or floods, the scientists suggest—before being released in the Bengal Fan.
The team say this is the first evidence showing trees can be transported for thousands of miles, from mountains to the deep ocean. Their findings also shed light on the role of wood in Earth's carbon cycle—the way carbon travels from the atmosphere into the planet and its organisms, and back out again.
Carbon stored in plants is released when it is eaten, decays or is burned. Because the trees were transported shortly after being uprooted—the point of death—they did not decompose. Instead, the fresh wood was locked into the seafloor sediment—potentially representing a previously unrecognized means by which carbon can be stored for millions of years.
"The discovery of woody fragments in the coarse-grain layers of turbidite beds across 19 [million years] indicates that woody input may be a neglected contributor to the [organic carbon] cycle in the Bengal Fan and in other continental margins over geologic timescales," the researchers wrote, adding that the findings suggest the organic carbon locked in continental margins may be higher than once thought. "The rapid export and burial of wood represents a highly efficient pathway of atmospheric CO2 sequestration," they said.
Understanding how much carbon may be locked away as a result of forests being washed into the ocean is important in understanding future climate change, Fearkins said. "As we've tried to calculate the amount of carbon in all parts of the carbon cycle, we didn't know about this forest of fragmented trees buried in the ocean floor," she said in a statement. "Now we need to add it to the equation."
Scientists are currently working to understand the carbon cycle, with researchers in the U.S. launching the Deep Carbon Observatory (DCO) over a decade ago. A report recently released by the group showed that less than 1 percent of Earth's total carbon is above surface—in the oceans, on land and in the atmosphere. The rest is all locked away in the planet's crust, mantle and core.
Stock photo showing the Bay of Bengal. Researchers drilled down two miles under the surface of the ocean to find evidence of ancient trees being washed thousand of miles out to sea.
