Enrichment and constraints of critical metals in ferromanganese crusts from 13°20'N seamount of the southern Kyushu-Palau Ridge
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摘要: 铁锰结壳富集Co、Cu、Mn、Ni、Ti、V、REE、Y和Zn等关键金属,研究其富集于结壳的规律以及相关地质环境制约因素对于未来开发利用这些海底金属资源十分重要。本文对九州-帕劳海脊南部13°20′N新发现的铁锰结壳样品进行了矿物学、元素地球化学和电子探针微区分析,发现其成分较为均一,未遭受明显的磷酸盐化作用,属于单层型水生成因结壳。Co、Ni等高含量关键金属主要富集在水羟锰矿内,其中主要以晶格态形式存在的Co所经历的表面氧化还原反应是其累积富集的关键;而Ni除了与Co一样通过置换Mn或占据晶格空位而呈现富集特征外,还大量以吸附态形式存在。Ti、V和REY等通过表面络合、晶格进入以及共沉淀作用富集在以六方纤铁矿为主的铁羟基氧化物组分内。Cu、Zn的晶格进入能力不足,加之海水Cu含量偏低,Zn的弱吸附作用共同导致它们以相对低含量形式分散分布。基于Co经验公式揭示结壳的形成起始于晚中新世,未出现明显生长间断,但持续生长时间不足导致结壳的关键金属累积富集程度低于全球主要结壳成矿区。不过,研究区理想的水深条件、较低的沉积速率、稳定的构造环境、合适的最小含氧带水深分布和远离非成矿物质的大规模稀释影响,都是本区结壳未来持续性增生和进一步富集关键金属的有利条件。Abstract: Ferromanganese crusts are highly enriched in a wide variety of critical metals including Co, Cu, Mn, Ni, Ti, V, REE, Y, and Zn. Study of their enrichment in the crusts and the geological constraints is important for future development and utilization of them at seafloor. Recently, ferromanganese crust samples were acquired from 13°20′N seamount of the southern Kyushu-Palau Ridge, and analyzed in mineralogy and element geochemistry, as well as for electron probe microanalysis. Results show that the mineralogical and chemical composition of the samples are relatively uniform, and the crusts have not suffered from obvious phosphatization, which indicates that the crusts are characterized by one hydrogenetic crustal layer. Critical metals with high content such as Co and Ni are mainly enriched in vernadite. Co mainly exists in the lattice of vernadite due mainly to surface oxidation of vernadite. Ni is enriched in the crusts by replacing and occupying lattice vacancies of Mn as Co does, and a large amount of Ni exists in the form of adsorption. Ti, V, and REY are enriched in the iron oxyhydroxide components dominated by feroxyhyte by surface complexation, crystal lattice entry, and co-precipitation. Cu and Zn are lack of crystal lattice entry ability; the Cu content in seawater is very low and the adsorption of Zn is weak, thus resulting in their dispersed distribution and low content in the samples. This study reveals that the crusts started growing in the late Miocene and show no obvious growth break; the accumulated enrichment degree of critical metals in these samples is lower than that in the highest potential areas of the global ocean due to insufficient continuous growth time. However, the ideal water depth conditions, low deposition rate, stable tectonic environment, suitable water depth distribution of the oxygen minimum zone, and long distance from macroscale input of the non-metallogenic material into the study area are favorable for continuous growth and enrichment of critical metals in these crusts in the future.
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Keywords:
- ferromanganese crusts /
- critical metals /
- enrichment principles /
- constraints /
- Kyushu-Palau Ridge
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渤海湾毗邻现代黄河三角洲,沿岸主要为砂质淤泥质海岸,其沉积物主要来自沿岸河流携带的大量泥沙,受河流与沿岸细粒物质大量供给和潮流作用为主的海洋动力控制,呈不规则带状和斑块状分布,沿岸粒度较粗,多为粉砂和黏土粉砂,东北部沿岸多为砂质粉砂,中部海域粒度较细,多为黏土软泥和粉砂质软泥[1]。渤海湾沿岸有多条河流,如黄河、海河、滦河等,其中黄河和滦河是渤海湾沉积物的主要来源[2],并以黄河入海泥沙量最大[3]。黄河每年入海泥沙约11亿t,大量入海泥沙在黄河口沉积下来,不仅使河流入海流路发生频繁变迁,而且导致河口三角洲快速淤积[4-7]。在海洋动力作用下,大量细颗粒泥沙自黄河口三角洲向北、东北、西北方向海域传输,可达到渤海湾湾顶[8-9]。自1976年以来其北部废弃的三角洲叶瓣遭受强烈的海岸侵蚀,在冬季强海洋动力作用下,大量再悬浮沉积物为渤海湾区域提供充足的物源供应[3,10-11]。随着人类活动的增强,河流入海径流量和泥沙量明显减少,粒度粗化[6,10,12],大量泥沙快速沉积在河口附近,在波浪和潮流的控制下,泥沙再悬浮并在渤海海域传输,在沿岸悬浮体浓度明显高于渤海湾中部[13-14],水体底层浓度明显高于表层浓度,悬浮体浓度的分布呈季节性分布特征[3,11,15-16],冬季渤海湾在强风浪的再悬浮和沿岸流的搬运作用下,悬浮体浓度分布明显高于海洋动力较弱的夏季[3,17-18],水体的层化混合过程对黄河入海悬浮体传输过程起到重要的控制作用[6,19]。除此之外,渤海湾海域悬浮体的分布还具有明显的大小潮差异,大潮时期悬浮体浓度高于小潮时期[20]。因此,不同时段、不同区域内,渤海湾海域悬浮体的分布特征与海域内海洋动力条件有着密不可分的关系,要了解该海域悬浮体分布的变化规律,就需要分不同时段对不同区域进行连续观测研究,才能更全面地掌握渤海湾悬浮体的运移特征。但是迄今为止对黄河三角洲北部和渤海湾泥质区毗邻海域再悬浮沉积物的输运过程及其沉积分布尚缺乏系统性观测研究,这方面的观测有待加强。大量的研究表明[21-23],近海沉积物输运过程及其沉积分布与污染物和生源要素的扩散具有极为密切的关系,是影响区域生物地球化学循环和生态系统的重要因素。渤海湾周边城市人口稠密,大中城市密集,有重要能源生产基地,是目前我国重要的经济发展区之一。随着大规模的围海造地工程和周边临港工程建设,填海面积增加的同时,大量来自陆域的重金属和污染物较易附着在悬浮体上随径流入海,并在海洋动力的作用下,在近岸海域扩散和沉积,对近岸海洋生态系统产生了重要影响[24-27]。因此渤海湾及毗邻海域不同时间尺度的沉积动力过程及其环境效应,有利于推进对该海域沉积动力学和“源–汇”过程研究的进一步认识,对区域环境可持续发展具有重要的意义。
本文在前人的研究基础上,对渤海湾泥质区南部靠近黄河三角洲北部海域的夏季悬浮体浓度、水体温盐结构进行了25 h连续观测调查,对悬浮体输运过程展开了时空对比分析,并探讨了其水动力机制。
1. 材料及方法
1.1 数据采集
2012年8月20日—9月10日在渤海湾海域完成了对10个站位的海流连续25 h定点观测,并每隔1 h对垂向剖面进行温度、盐度和浊度的观测,采集表、中、底3层水位的悬浮体水样用于悬浮体浓度的实验室抽滤测试分析(图1)。其中,流速、流向及水深数据采集使用美国SonTek公司生产的声学多普勒流速剖面仪ADCP(工作频率为300 kHz,盲区为1 m,测流误差<5 mm/s和<1°)来进行观测,测层间隔设置为1 m,定点观测采样频率设为10 s,温度、盐度及浊度数据采集使用美国Seabird公司生产的SBE19 Plus多参数水质剖面仪来进行观测(温度、电导率和浊度的精度分别为<0.1°C、0.001 mS/cm和0.01 NTU),用绞车以平均每2 s下放1 m的速度下放仪器,平均每0.2 s可获取一个数据,悬浮体水样采集使用美国Seabird公司生产的SBE ECO55自动采水器进行采集,该仪器与SBE19 Plus集成在一起。悬浮体水样采集以ADCP测深为准,分层进行采取(表层样取自水深2 m以内,中层样取自0.5倍水深处,底层样取距底0.5~2 m处),与温度、盐度及浊度数据采集同步进行。本文采用本航次调查的10个站位中位于渤海湾泥质区南部的5个站位(A1—A5站)的观测结果进行悬浮体输运过程分析。
1.2 数据处理
悬浮体水样在实验室进行双滤膜抽滤测试,抽滤实验采用孔径0.45 μm的醋酸纤维滤膜进行双膜抽滤矫正,抽滤前将滤膜以45°C烘干24 h并称得上膜前质量(Wt1)和下膜前质量(Wb1),称重采用万分之一的电子天平,抽滤后再以45°C烘干24 h并称得上膜后质量(Wt2)和下膜后质量(Wb2),并记录抽滤水体体积(V)通过计算公式(1)计算悬浮体浓度(SSC)。
$${\rm{ SSC}} =\frac{W_{\rm{t2}}-W_{\rm{t1}}-\dfrac{(W_{\rm{b2}}-W_{\rm{b1}})\times W_{\rm{t1}}}{W_{\rm{b1}}}}{V} $$ (1) 选取10个站位SSC测试结果,对采集悬浮体样品所在的垂向2 m范围内的悬浮体浊度进行平均计算,并与SSC进行拟合,拟合结果如图2所示,相关系数R2=0.83,拟合结果较好,可参考拟合结果,根据悬浮体浊度的观测结果,对SSC进行拟合判定。
2. 结果
2.1 潮流特征
渤海湾泥质区南部潮流以M2潮流为主[29-30],从图3和图4的流速矢量图以及图3潮流类型分布[29]可以看出,A1、A2、A3、A5站的潮流类型为规则半日潮流,A4站潮流类型为不规则半日潮流,A1站为逆时针旋转流,A2站为E-W向往复流,A3、A4、A5站为顺时针旋转流。从图4水深变化以及图3潮汐类型分布[29]可以看出,A1、A2、A4站的潮汐类型为不规则半日潮,A3站为不规则全日潮,A5站处在不规则全日潮的位置,而在观测期间,A5站出现半日潮特征。各站位的流速东西分量u明显高于流速南北分量v(图4),u分量流速超过40 cm/s的历时超过观测历时的1/2,v分量流速低于40 cm/s的历时占观测历时的主要部分。A1站涨潮流为SW向,落潮流为NE向;A2站涨潮流为W向,落潮流为E向;A3站涨潮流和落潮流均有N向顺时针旋转为E向的现象;A4站涨潮流为SE向顺时针旋转为NW向,落潮流为NW向顺时针旋转为SE向;A5站涨潮流和落潮流均有NW向顺时针旋转一周回到NW向的现象。
2.2 温盐交换过程
从各站位温盐垂向剖面结构可以看出(图5),受各站位涨落潮流影响,水体的垂向温盐结构具有周期性分布的特点。整体来看(图6),水深最浅、最靠近岸边的A1站(水深5~15 m)温度最高,盐度最低,水深15~20 m的A2站和A5站温度和盐度都偏高,水深大于20 m的A3站和A4站温度偏低,盐度偏高。这说明渤海湾泥质区南部海域,15 m等深线以浅海域受周边径流高温淡水影响较大,15~20 m范围高温淡水与低温盐水交汇,盐度明显升高,20 m以深海域主要受渤海中部低温高盐水舌入侵影响,水体温度偏低。
A1站SW向涨潮流从湾外带来低温高盐的水体,NE向落潮流向湾外带走近岸的高温低盐的水体;湾口处A2站W向涨潮流从湾外带来低温高盐水体,E向的落潮流从湾内带出高温低盐水体,主要在表层水深10 m范围内传输,10 m以深水体为盐度较高、温度较低的水体;A3站的温盐结构在涨潮和涨平阶段,在表层10 m范围内层化明显,出现高温低盐水体,10 m以深水体垂向较均匀,在落潮和落平阶段,水体温盐垂向结构整体均匀,主要为温度和盐度都相对较高的水体;A4站和A5站的温盐结构较其他站位更稳定,温度自上而下逐渐降低,盐度自上而下逐渐升高,A4站(站位水深约25 m)在水深15 m(自海面向下)处温盐梯度较大,A5站(站位水深约20 m)则是在水深10 m处温盐梯度较大,两站连线与黄河口附近岸线和等深线接近垂直,呈NE向展布,说明夏季黄河口高温低盐的淡水向20 m以深的渤海中部海域传输的方式,主要为表层传输的羽状流形式。
2.3 SSC时空变化特征
从图7可以看出,渤海湾内(A1站)和湾口(A2站)处高浊度悬浮体多出现在涨急和落急时期,较高的流速对底质掀沙作用加强(图8a),其中A1站涨平后到落急期间SSC明显降低,可见,在渤海湾南部湾内的近岸海域,大部分底质再悬浮的泥沙还是随着涨潮流向湾内汇聚,方向多为SW向。黄河口SE向的A3、A4、A5三站SSC分布的潮周期特点较湾内和湾口处不显著,且水体较湾内和湾口清澈,SSC值偏低。A3站SSC高值出现在N向和E向潮流时期,A4和A5站SSC高值出现在NW向和SE向潮流时期。
整体来看(图8a),夏季渤海湾南部海域高于20 mg/L的SSC值出现在A2、A3站表层5 m水深范围内,A3、A4、A5站底层5 m水深范围内,A2站底层12 m范围内,以及A1站的整个垂向水体范围内。靠近底层的SSC值均高于表层SSC值(图8a),各站位靠近底层最高SSC值对比结果显示,湾内(A1站)及湾口(A2站)处最高,分别可达约130和80 mg/L,黄河口SE向20 m及更深(A4、A5站)处最小,均低于40 mg/L。SSC值高于20 mg/L的流速值基本位于50~70 cm/s区间(图8b),各站位流速基本低于100 cm/s,结合图8a,可知该区域底层高浊度的悬浮细颗粒物质的输运流速在50~100 cm/s区间,且具备这种输运条件的高浊度悬浮体多出现在渤海湾南部湾内和湾口海域,其向湾内汇沙的效应也符合中国东部陆架边缘海沉积物“夏储冬输”的季节性特征[31]。
3. 讨论
3.1 悬浮体输沙率的潮周期变化特征
采用相对水深对瞬时物质输移量进行分解[32],设x轴为纵向坐标,t为时间,z为相对水深(0≤z≤1),不计流速脉动项,将瞬时流速u(x, z, t)分解成垂向平均量项及其偏项之和:
$$ u(x, z, t)=\bar u+u' $$ (2) ū和uʹ均分解为潮平均量项和潮变化项之和:
$$\bar u= \bar u_{0}+\bar u_{t}·u'=\bar u_{0}'+\bar u_{t}'$$ (3) 瞬时流速即为:
$$ u(x, z, t) = \bar u_{0}+\bar u_{t}+\bar u_{0}'+\bar u_{t}'$$ (4) 水深可分解为:
$$ h(x, t)= h_{0}+h_{t} $$ (5) 单宽潮周期平均输水量为:
$$ \langle Q \rangle = \frac{1}{T_t}\int\limits ^{T_t}_0\int\limits^1_0 uh{\rm d}z{\rm d}t= \bar u_{0}h_{0}+ \langle \bar u_{t}h_{t} \rangle$$ (6) 其中,
$\langle \rangle$ 表示潮平均,ū0h0为平均流项,$ \langle$ ūtht$\rangle $ 为潮汐与潮流相关项,即斯托克斯漂移效应,Tt为潮周期。式(6)可表示为:$$\langle Q \rangle = h_{0}(\bar u_{E}+\bar u_{S}) = h_{0}\bar u_{L} $$ (7) 其中,ūE = ū0,ūS =
$\langle $ ūtht$\rangle $ /h0$$ \bar u_{L}=\langle Q\rangle/h_{0} =\bar u_{E}+\bar u_{S} $$ (8) 由式(8)计算出来的ūL即为一维垂向平均拉格朗日余流,其中ūE、ūS分别为一维垂向平均欧拉余流和斯托克斯余流。
与余流的计算原理相似(式(2)—(5)),悬浮泥沙浓度SSC的函数c(x, z, t)可分解为:
$$ c(x, z, t) =\bar c_0 +\bar c_t +c_{0}'+c_{t}' $$ (9) 单宽输沙率E为:
$$\begin{split}\int\limits ^1_0 huc{\rm d}z =& h\bar u_{0}\bar c_0+h\bar u_{0}\bar c_t+h\bar u_{t}\bar c_0+h\bar u_{t}\bar c_t+\\&h\overline{u'_0c'_0}+h\overline{u'_0c'_t}+h\overline{u'_tc'_0}+h\overline{u'_tc'_t}\end{split} $$ (10) 其中,E1=
$h\bar u_0 \bar c_0 $ 为平流引起的平均输沙量,$E_2=h\bar u_0\bar c_t $ 和$E_3=h\bar u_t\bar c_0 $ 为潮周期平均输沙量与潮变化量的相关项,$E_4=h\bar u_t\bar c_t $ 为潮汐振荡引起的输沙量,$E_5=h\overline{u'_0c'_0} $ 为时均量引起的扩散,$E_6=h\overline{u'_0c'_t} $ 和$E_7=h\overline{u'_tc'_0} $ 为时均量与潮变化量引起的剪切扩散,$E_8=h\overline{u'_tc'_t} $ 为潮振荡引起的剪切扩散。潮平均单宽瞬时输沙率T为:
$$ \begin{split} T=& \frac{1}{T_t}\int\limits^{T_t}_0\int\limits^h_0 uc{\rm d}z{\rm d}t=h_{0}\bar u_{0}\bar c_0+\langle h_{t}\bar u_{t}\rangle \bar c_0+\langle h_{t}\bar c_t \rangle \bar u_{0}+\\&\langle h_{t}\bar u_{t}\bar c_t\rangle + h_{0}\overline{u'_0c'_0} +\langle h_{t} u'_{0}c'_{t}\rangle +\langle h_{t}u'_{t}c'_{0}\rangle +\langle h_{t}u'_{t}c'_{t}\rangle \end{split} $$ (11) 其中,
$T_1=h_0\bar u_0\bar c_0 $ 为平均流引起的输沙量;$T_2=\langle h_t\bar u_t \rangle \bar c_0 $ 为潮汐与潮流的相关项,即斯托克斯漂流输沙量;T1+T2为拉格朗日输沙量;$T_3=\langle h_t \bar c_t \rangle \bar u_0$ 为潮汐与含沙量潮变化相关项;$T_4=\langle h_t \bar u_t \bar c_t \rangle $ 为SSC与潮流变化相关项;$T_5=h_0\overline{u'_0 c'_0} $ 为垂向流速变化和含沙量变化的相关项,为垂向净环流的贡献;$ T_6=\langle h_t u'_0 c'_t \rangle $ 和$T_7=\langle h_tu'_tc'_0 \rangle $ 为时均量与潮汐振动切变引起的剪切扩散;$T_8=\langle h_t u'_t c'_t \rangle $ 为垂向潮振荡切变作用项。湾内A1站(图9a)涨平期间的单宽输沙率为68~143 g·m−1·s−1,方向为偏S向,向岸输沙。落平期间单宽输沙率为41~93 g·m−1·s−1,方向为偏N向,向湾外输沙,单宽输沙率明显小于涨平期间。落潮时期输沙以E、SE向为主,涨潮时期输沙率方向以W、SW向为主,大小相当。整体来看(图10a),渤海湾南部湾内海域以向近岸输沙为主,潮平均单宽输沙率为7.8 g·m−1·s−1,方向为280°(以E向为0°的逆时针旋转角度),其中,T1+T2所代表的拉格朗日输沙率为7.6 g·m−1·s−1,方向为274°;T4和T5数量级相当,分别为0.6和0.3 g·m−1·s−1,方向为偏E向和偏SE向;其他分量的数量级较小,T3、T6数量级相当,T7和T8数量级相当,T3、T6、T7方向偏E向和偏SE向,T8方向偏N向。
湾口A2站(图9b)落平和落潮时期输沙方向偏E向,以朝湾外输沙为主,在涨平和涨潮期间输沙方向偏W向,以向湾内输沙为主,前者的单宽输沙率范围为24~281 g·m−1·s−1,后者的单宽输沙率范围为28~258 g·m−1·s−1,后者历时更长。整体上(图10b),湾口处海域拉格朗日输沙率(T1+T2)为12.7 g·m−1·s−1,方向为329°;垂向净环流的贡献项T5为5.5 g·m−1·s−1,方向为149°,方向与拉格朗日输沙率方向相反;整体来看A2站潮平均输沙率为7.2 g·m−1·s−1,方向为328°,输沙以向湾外SE向输沙为主;其他分量数量级较小,T4和T7数量级相当,T3、T6、T8数量级最小,T3、T6、T7方向偏SE向,T4和T8方向偏NW向。
A3站(图9c)落平时输沙以偏E向为主(18~46 g·m−1·s−1),涨平时输沙以偏SE向为主(10~54 g·m−1·s−1),涨潮时输沙以偏W向为主(12~59 g·m−1·s−1),落潮时输沙以偏N向和偏NE向为主(5~44 g·m−1·s−1)。整体来看(图10c),A3站潮平均单宽输沙率为4.7 g·m−1·s−1,方向为77°,其中,拉格朗日输沙率(T1+T2)为5.2 g·m−1·s−1,方向为50°;垂向净环流的贡献项T5为2.4 g·m−1·s−1,方向为166°;T3、T4数量级相当,T6、T7、T8数量级最小,T4、T7方向偏E向,T6偏SE向,T3、T8偏SW向。
A4站(图9d)涨潮时输沙偏SE向,单宽输沙率为8~49 g·m−1·s−1;涨平时输沙偏NW向,单宽输沙率为19~52 g·m−1·s−1;落潮时输沙偏NW向,单宽输沙率为29~56 g·m−1·s−1;落平时输沙偏N向和偏NE向,单宽输沙率为11~51 g·m−1·s−1。A4站潮平均单宽输沙率为5.2 g·m−1·s−1,方向为94°,其中,拉格朗日输沙率(T1+T2)为5.2 g·m−1·s−1,方向为91°,其他各分量数量级较小,T3和T7方向相反,数量级相当;T4数量级与T3和T7相当,方向为偏NW向;T5数量级比T3大,方向为偏W向;T6数量级与T3相当,方向为偏NE向;T8数量级比T3小,方向为偏SE向。
A5站(图9e)落潮时输沙偏NW向,单宽输沙率为50~88 g·m−1·s−1;落平时单宽输沙率为32~78 g·m−1·s−1,方向自偏NW向顺时针旋转至偏SE向;涨潮时输沙偏SE向,单宽输沙率为37~105 g·m−1·s−1;涨平时单宽输沙率为7~55 g·m−1·s−1,输沙偏NW向。A5站潮平均单宽输沙率为7.7 g·m−1·s−1,方向为102°,其中,拉格朗日输沙率(T1+T2)为8.8 g·m−1·s−1,方向86°;垂向净环流的贡献项T5为2.5 g·m−1·s−1,方向208°;其他各分量数量级较小,其中T4数量级最大,方向偏E向,T3、T6、T7、T8数量级相当,T3、T7方向偏NE向,T6、T8方向偏SW向。
整体来看,渤海湾南部各站位潮平均单宽输沙率以拉格朗日输沙贡献最显著,在湾口泥质区南部和东南部水深15~25 m的海域,垂向净环流的影响较大,有抵消一部分拉格朗日输沙率的作用,且对潮平均单宽输沙率的影响比湾内和25 m以深海域的大,其中对A2站的拉格朗日输沙率的抵消作用最大,这跟A2站垂向净环流输沙率较大,且方向与拉格朗日输沙率相反有关。其他分量数量级较小,对潮平均单宽输沙率贡献较小。由于本次观测站位非同步连续观测,时间跨度较大,部分站位观测的是小潮时期的输沙率(A1、A2、A3站),另一部分站位观测的是大潮时期的输沙率(A4、A5站),因此对各站位之间输沙率的比较还需要未来进一步开展同步观测调查。
3.2 水体层化混合过程与输沙率之间的相关性
水体的垂向混合状态可以用Richardson数来体现[6, 33-34],其计算公式如下:
$$ Ri =\frac{-\left(\dfrac{g}{\rho}\right)\left(\dfrac{\partial\rho}{\partial z}\right)}{\left(\dfrac{\partial u}{\partial z}\right)^2} $$ (12) 其中,分子表示水体密度梯度导致的层化强度,分母表示水体剪切力所导致的湍动混合程度,Ri>0.25,代表水体以层化为主,Ri<0.25,代表水体以混合为主。结果如图11所示,结合图5的温盐结构来看,A1、A2、A3、A4站受近岸高温低盐水体影响,这4个站位的密度结构不稳定,层化强度和Ri值多数时刻为负,相应时刻对应的混合程度较高。Ri值整体以小于0.25为主,说明渤海湾南部海域水体以混合为主,单宽输沙率降低的时刻,与水体层化程度和Ri值增加的时刻相吻合,如A1站的0时、14时、20时,A2站的5时、18时、23时,A3站的4时、14时,A4站的5时、17时、23时,A5站的6时、11时、12时、17时、18时、22时,可见水体的层化程度加强对各站位悬浮体输运均有一定的抑制作用,这与黄河口、加利福尼亚北部的大陆架和福宁湾海域前人研究结论相符[6, 35-36]。
4. 结论
(1)受周边径流高温淡水影响,夏季渤海湾南部及黄河三角洲北部15 m以浅海域水体温度较高,盐度较低;15~20 m范围内高温淡水与低温盐水交汇,水体盐度明显升高;20 m以深海域主要受渤海中部低温高盐水舌入侵影响,水体温度偏低。高温淡水以羽状流的方式自近岸向渤海中部传输。渤海湾内和湾口处高浊度悬浮体多出现在涨急和落急时期,较高的流速对底质的再悬浮作用加强,距底5 m水深范围内SSC值较高,其中湾内和湾口的底层SSC值最高,黄河口外NE向剖面20 m以深海域SSC值最小。
(2)渤海湾泥质区南部海域夏季单宽输沙率具有潮周期性特点。湾内海域涨潮和涨平期以向湾内近岸输沙为主,落潮和落平期以向湾外输沙为主,整体以向湾内近岸输沙为主,潮平均单宽输沙率为7.8 g·m−1·s−1,方向为280°。湾口A2站涨落潮流输沙方向相反,整体以SE向朝湾外近岸输沙为主,潮平均单宽输沙率为7.2 g·m−1·s−1,方向为328°。湾外A3站涨潮和涨平时期输沙方向基本相反,大小相当,落潮和落平时期输沙方向以偏E和偏NE向为主,潮平均单宽输沙率为4.7 g·m−1·s−1,方向为77°。黄河口SE向的2个站位涨潮时输沙偏SE向,涨平时输沙偏NW向,落潮时输沙偏NW向,落平时输沙偏N向和偏NE向,两站潮平均单宽输沙率方向以偏N向为主,A4站潮平均单宽输沙率为5.2 g·m−1·s−1,方向为94°,A5站潮平均单宽输沙率为7.7 g·m−1·s−1,方向为102°。
(3)渤海湾泥质区南部各站位夏季潮平均单宽输沙率以拉格朗日输沙贡献最显著,在湾口泥质区南部和东南部水深15~25 m海域,垂向净环流的影响较大,有抵消一部分拉格朗日输沙率的作用,且对潮平均单宽输沙率的影响比湾内和25 m以深海域的大,其他分量数量级较小,对潮平均单宽输沙率贡献较小。
(4)渤海湾泥质区南部海域夏季水体以混合为主,各站位水体层化程度加强对各站位悬浮体输运均有一定的抑制作用。
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图 4 结壳样品REY的PAAS标准化配分模式
为便于显示,将海水的REY值扩大106倍;PAAS的REY含量引自文献[20]。海水的REY含量数据选择与本研究区临近且水深层位相近的海水的值,其中REE数据引自文献[21],采样区域为本研究区东面的西太平洋,水深2000 m;Y数据引自文献[22],采样区域为西南太平洋东加罗林海盆,水深1980 m。
Figure 4. Shale normalized rare earth elements and yttrium contents of the ferromanganese crusts
To facilitate the display in the diagram, the REY contents of the seawater are expanded by 106 times; PAAS data are from the reference [20]. The REY data of the seawater is from the reference [21], the sampling area with the water depth of 2000 m is in the western Pacific Ocean close the study area, which is similar to the distribution depth of the samples in this paper. Y data of the seawater is from the reference [22]. The sampling area was in the east Caroline Basin of the southwest Pacific Ocean, in water depth of 1980 m.
图 6 本文研究区与全球结壳主要成矿区内样品的关键金属平均含量对比
PCZ、NPCZ、南太平洋、印度洋和大西洋铁锰结壳样品的成分数据引自文献[6]。
Figure 6. Mean contents of the critical metals in the ferromanganese crusts from the research area and the highest potential areas of the global ocean
The contents of the critical metals in the ferromanganese crusts of the PCZ, NPCZ, South Pacific, Indian, and Atlantic Ocean are from the reference[6].
表 1 结壳样品元素含量特征
Table 1 Chemical composition of the ferromanganese crusts
元素 外层 中间层 内层 基质 Al/% 1.58 1.69 1.98 7.97 Ca/% 2.31 2.36 2.41 4.26 Fe/% 17.70 18.78 18.52 11.20 Mn/% 20.68 19.44 18.67 1.35 P/% 0.23 0.23 0.22 0.09 Si/% 5.92 6.47 7.01 21.29 Ti/% 0.94 1.08 1.03 0.76 Ce/10−6 692 764 717 94 Co/10−6 3400 3220 3090 156 Cu/10−6 1120 853 927 373 Ni/10−6 3400 2620 2720 291 V/10−6 547 515 491 261 Zn/10−6 512 463 491 276 LREY/10−6 1230 1322 1202 173 HREY/10−6 274 258 229 60 REY/10−6 1503 1579 1431 233 表 2 样品不同层位铁锰氧化物的电子探针微区成分数据
Table 2 Element contents in the ferromanganese oxides layers from different parts of the sample revealed in electron probe microanalysis
元素 Al Ca Ce Co Cu Fe Mn Ni P Si Ti V Zn 外层
(n=13)最大值/% 1.62 3.04 0.16 0.73 0.18 24.37 28.61 1.10 0.45 3.70 1.32 0.13 0.10 最小值/% 0.43 1.62 0.05 0.24 0.09 16.84 22.98 0.42 0.30 2.07 0.64 0.07 0.05 平均值/% 0.64 2.47 0.13 0.59 0.14 19.25 26.81 0.65 0.36 2.62 1.16 0.09 0.08 离散系数/% 45.98 16.64 21.87 23.60 19.89 10.58 6.06 24.58 12.97 17.90 14.80 17.29 17.38 中间层
(n=20)最大值/% 1.22 2.89 0.16 0.74 0.22 24.81 32.27 0.82 0.47 4.93 1.38 0.12 0.11 最小值/% 0.34 2.05 0.09 0.26 0.07 17.01 22.72 0.40 0.30 1.59 1.00 0.07 0.01 平均值/% 0.67 2.54 0.13 0.50 0.14 21.06 26.50 0.58 0.38 2.92 1.21 0.10 0.07 离散系数/% 29.34 7.88 14.57 25.34 24.59 11.22 9.67 23.00 14.48 26.75 8.97 13.66 33.77 内层
(n=20)最大值/% 1.77 2.61 0.19 0.75 0.20 35.47 30.66 0.75 0.48 6.40 3.14 0.14 0.14 最小值/% 0.49 1.05 0.10 0.20 0.08 16.36 11.02 0.15 0.28 1.88 1.13 0.07 0.06 平均值/% 0.85 2.24 0.15 0.42 0.13 23.71 23.83 0.43 0.39 3.62 1.44 0.11 0.09 离散系数/% 41.40 17.22 16.12 27.84 22.63 15.34 15.92 29.60 13.75 25.83 29.81 15.91 25.82 表 3 微区铁锰氧化物纹层内各元素间的相关系数矩阵(n=53)
Table 3 Pearson correlation coefficient matrix for major and valuable metal elements contained in the ferromanganese oxide layers (n=53)
Al Ca Ce Co Cu Fe Mn Ni P Si Ti V Ca −0.78 Ce 0.12 −0.07 Co −0.67 0.57 −0.21 Cu −0.01 0.18 −0.13 −0.04 Fe 0.49 −0.43 0.60 −0.69 −0.06 Mn −0.72 0.67 −0.41 0.75 0.06 −0.90 Ni −0.48 0.45 −0.45 0.65 0.13 −0.82 0.77 P 0.09 0.08 0.35 −0.47 −0.01 0.68 −0.52 −0.64 Si 0.78 −0.64 0.38 −0.72 −0.04 0.87 −0.94 −0.76 0.52 Ti 0.53 −0.55 0.53 −0.37 −0.04 0.76 −0.76 −0.55 0.18 0.72 V −0.03 0.06 0.41 −0.30 0.11 0.68 −0.49 −0.50 0.63 0.46 0.40 Zn 0.17 −0.10 0.12 −0.45 0.15 0.44 −0.39 −0.47 0.50 0.40 0.12 0.45 -
[1] Hein J R, Koschinsky A. 13. 11 - Deep-ocean ferromanganese crusts and nodules[M]//Holland H D, Turekian K K. Treatise on Geochemistry. 2nd ed. Oxford: Elsevier, 2014: 273-291.
[2] Petersen S, Krätschell A, Augustin N, et al. News from the seabed – geological characteristics and resource potential of deep-sea mineral resources [J]. Marine Policy, 2016, 70: 175-187. doi: 10.1016/j.marpol.2016.03.012
[3] Halbach P E, Jahn A, Cherkashov G. Marine Co-Rich ferromanganese crust deposits: description and formation, occurrences and distribution, estimated world-wide resources[M]//Sharma R. Deep-Sea Mining. Cham: Springer, 2017: 65-141.
[4] Li Y H, Schoonmaker J E. 9.1 - Chemical composition and mineralogy of marine sediments [M]//Holland H D, Turekian K K. Treatise on Geochemistry. 2nd ed. Oxford: Elsevier, 2014: 1-32.
[5] White W M, Klein E M. 4.13 - Composition of the oceanic crust[M]//Holland H D, Turekian K K. Treatise on Geochemistry. 2nd ed. Oxford: Elsevier, 2014: 457-496.
[6] Mizell K, Hein J R, Au M, et al. Estimates of metals contained in abyssal manganese nodules and ferromanganese crusts in the global ocean based on regional variations and genetic types of nodules [M]//Sharma R. Perspectives on Deep-Sea Mining: Sustainability, Technology, Environmental Policy and Management. Cham: Springer, 2022: 53-80.
[7] 李三忠, 赵淑娟, 索艳慧, 等. 区域海底构造-上册[M]. 北京: 科学出版社, 2021. LI Sanzhong, ZHAO Shujian, SUO Yanhui, et al. Regional Submarine Tectonics-Volume One[M]. Beijing: Science Press, 2021.
[8] Ishizuka O, Taylor R N, Yuasa M, et al. Making and breaking an island arc: A new perspective from the Oligocene Kyushu-Palau arc, Philippine Sea [J]. Geochemistry, Geophysics, Geosystems, 2011, 12(5): Q05005.
[9] 张洁, 李家彪, 丁巍伟. 九州-帕劳海脊地壳结构及其形成演化的研究综述[J]. 海洋科学进展, 2012, 30(4):595-607 doi: 10.3969/j.issn.1671-6647.2012.04.016 ZHANG Jie, LI Jiabiao, DING Weiwei. Reviews of the study on crustal structure and evolution of the Kyushu-Palau ridge [J]. Advances in Marine Science, 2012, 30(4): 595-607. doi: 10.3969/j.issn.1671-6647.2012.04.016
[10] Yamazaki T, Takahashi M, Iryu Y, et al. Philippine Sea Plate motion since the Eocene estimated from paleomagnetism of seafloor drill cores and gravity cores [J]. Earth, Planets and Space, 2010, 62(6): 495-502. doi: 10.5047/eps.2010.04.001
[11] Party Shipboard Scientific. Initial reports of the deep sea drilling project leg 59. Part I: introduction, site reports, 2, site 447: east side of the West Philippine Basin[R]. 1981.
[12] 何良彪. 马里亚纳海脊-西菲律宾海盆铁锰结核的地球化学[J]. 科学通报, 1991, 36(14):1190-1193 HE Liangbiao. Geochemical characteristics of Fe-Mn nodules and crusts from the Mariana ridge and the West Philippine Basin [J]. Chinese Science Bulletin, 1991, 36(14): 1190-1193.
[13] 陈穗田, Stüben D. 菲律宾海的锰结壳和锰结核[J]. 海洋学报, 1997, 19(4):109-116 CHEN Suitian, Stüben D. Manganese crusts and nodules in the Philippine Sea [J]. Acta Oceanologica Sinica, 1997, 19(4): 109-116.
[14] 徐兆凯, 李安春, 于心科, 等. 东菲律宾海新型铁锰结壳中元素的赋存状态[J]. 地球科学—中国地质大学学报, 2008, 33(3):329-336 doi: 10.3799/dqkx.2008.043 XU Zhaokai, LI Anchun, YU Xinke, et al. Elemental occurrence phases of the new-type ferromanganese crusts from the east Philippine Sea [J]. Earth Science—Journal of China University of Geosciences, 2008, 33(3): 329-336. doi: 10.3799/dqkx.2008.043
[15] Usui A, Graham I J, Ditchburn R G, et al. Growth history and formation environments of ferromanganese deposits on the Philippine Sea Plate, northwest Pacific Ocean [J]. Island Arc, 2007, 16(3): 420-430. doi: 10.1111/j.1440-1738.2007.00592.x
[16] Wegorzewski A V, Kuhn T. The influence of suboxic diagenesis on the formation of manganese nodules in the Clarion Clipperton nodule belt of the Pacific Ocean [J]. Marine Geology, 2014, 357: 123-138. doi: 10.1016/j.margeo.2014.07.004
[17] Heller C, Kuhn T, Versteegh G J M, et al. The geochemical behavior of metals during early diagenetic alteration of buried manganese nodules [J]. Deep Sea Research Part I:Oceanographic Research Papers, 2018, 142: 16-33. doi: 10.1016/j.dsr.2018.09.008
[18] Bau M, Schmidt K, Koschinsky A, et al. Discriminating between different genetic types of marine ferro-manganese crusts and nodules based on rare earth elements and yttrium [J]. Chemical Geology, 2014, 381: 1-9. doi: 10.1016/j.chemgeo.2014.05.004
[19] Josso P, Lusty P, Chenery S, et al. Controls on metal enrichment in ferromanganese crusts: Temporal changes in oceanic metal flux or phosphatisation? [J]. Geochimica et Cosmochimica Acta, 2021, 308: 60-74. doi: 10.1016/j.gca.2021.06.002
[20] McLennan S M. Rare earth elements in sedimentary rocks; influence of provenance and sedimentary processes [J]. Reviews in Mineralogy and Geochemistry, 1989, 21(1): 169-200.
[21] Deng Y N, Ren J B, Guo Q J, et al. Rare earth element geochemistry characteristics of seawater and porewater from deep sea in western Pacific [J]. Scientific Reports, 2017, 7(1): 16539. doi: 10.1038/s41598-017-16379-1
[22] Zhang J, Nozaki Y. Rare earth elements and yttrium in seawater: ICP-MS determinations in the East Caroline, Coral Sea, and South Fiji basins of the western South Pacific Ocean [J]. Geochimica et Cosmochimica Acta, 1996, 60(23): 4631-4644. doi: 10.1016/S0016-7037(96)00276-1
[23] Josso P, Pelleter E, Pourret O, et al. A new discrimination scheme for oceanic ferromanganese deposits using high field strength and rare earth elements [J]. Ore Geology Reviews, 2017, 87: 3-15. doi: 10.1016/j.oregeorev.2016.09.003
[24] Bonatti E, Kraemer T F, Rydell H. Classification and genesis of submarine iron-manganese deposits[M]//Horn D R. Ferromanganese Deposits on the Ocean Floor. New York: Arden House, 1972.
[25] 黄威, 胡邦琦, 徐磊, 等. 帕里西维拉海盆西缘中段铁锰结核的地球化学特征和成因类型[J]. 海洋地质与第四纪地质, 2021, 41(1):199-209 doi: 10.16562/j.cnki.0256-1492.2020101501 HUANG Wei, HU Bangqi, XU Lei, et al. Geochemical characteristics and genesis of the ferromanganese nodules in the middle western margin of the Parece Vela Basin [J]. Marine Geology & Quaternary Geology, 2021, 41(1): 199-209. doi: 10.16562/j.cnki.0256-1492.2020101501
[26] Peacock C L, Sherman D M. Vanadium(V) adsorption onto goethite (α-FeOOH) at pH 1.5 to 12: a surface complexation model based on ab initio molecular geometries and EXAFS spectroscopy [J]. Geochimica et Cosmochimica Acta, 2004, 68(8): 1723-1733. doi: 10.1016/j.gca.2003.10.018
[27] Millero F J, Woosley R, Ditrolio B, et al. Effect of ocean acidification on the speciation of metals in seawater [J]. Oceanography, 2009, 22(4): 72-85. doi: 10.5670/oceanog.2009.98
[28] GEOTRACES Intermediate Data Product Group. The GEOTRACES intermediate data product 2021 (IDP2021). NERC EDS British Oceanographic Data Centre NOC, 2021.
[29] Bruland K W, Middag R, Lohan M C. 8.2 - controls of trace metals in seawater[M]//Holland H D, Turekian K K. Treatise on Geochemistry. 2nd ed. Oxford: Elsevier, 2014: 19-51.
[30] Gong G C, Liu K K, Liu C T, et al. The chemical hydrography of the South China Sea West of Luzon and a comparison with the West Philippine Sea [J]. Terrestrial, Atmospheric and Oceanic Sciences, 1992, 3(4): 587-602. doi: 10.3319/TAO.1992.3.4.587(O)
[31] Behrens M K, Pahnke K, Schnetger B, et al. Sources and processes affecting the distribution of dissolved Nd isotopes and concentrations in the West Pacific [J]. Geochimica et Cosmochimica Acta, 2018, 222: 508-534. doi: 10.1016/j.gca.2017.11.008
[32] Manceau A, Drits V A, Silvester E, et al. Structural mechanism of Co2+ oxidation by the phyllomanganate buserite [J]. American Mineralogist, 1997, 82(11-12): 1150-1175. doi: 10.2138/am-1997-11-1213
[33] Manceau A, Lanson M, Takahashi Y. Mineralogy and crystal chemistry of Mn, Fe, Co, Ni, and Cu in a deep-sea Pacific polymetallic nodule [J]. American Mineralogist, 2014, 99(10): 2068-2083. doi: 10.2138/am-2014-4742
[34] Kuhn T, Wegorzewski A, Rühlemann C, et al. Composition, formation, and occurrence of polymetallic nodules[M]//Sharma R. Deep-Sea Mining: Resource Potential, Technical and Environmental Considerations. Cham: Springer, 2017: 23-63.
[35] Nozaki Y. A fresh look at element distribution in the North Pacific Ocean [J]. Eos, Transactions American Geophysical Union, 1997, 78(21): 221-221.
[36] Hens T, Brugger J, Etschmann B, et al. Nickel exchange between aqueous Ni(II) and deep-sea ferromanganese nodules and crusts [J]. Chemical Geology, 2019, 528: 119276. doi: 10.1016/j.chemgeo.2019.119276
[37] Peacock C L. Physiochemical controls on the crystal-chemistry of Ni in birnessite: Genetic implications for ferromanganese precipitates [J]. Geochimica et Cosmochimica Acta, 2009, 73(12): 3568-3578. doi: 10.1016/j.gca.2009.03.020
[38] Peacock C L, Sherman D M. Crystal-chemistry of Ni in marine ferromanganese crusts and nodules [J]. American Mineralogist, 2007, 92(7): 1087-1092. doi: 10.2138/am.2007.2378
[39] Wegorzewski A V, Grangeon S, Webb S M, et al. Mineralogical transformations in polymetallic nodules and the change of Ni, Cu and Co crystal-chemistry upon burial in sediments [J]. Geochimica et Cosmochimica Acta, 2020, 282: 19-37. doi: 10.1016/j.gca.2020.04.012
[40] Sherman D M, Peacock C L. Surface complexation of Cu on birnessite (δ-MnO2): Controls on Cu in the deep ocean [J]. Geochimica et Cosmochimica Acta, 2010, 74(23): 6721-6730. doi: 10.1016/j.gca.2010.08.042
[41] Little S H, Sherman D M, Vance D, et al. Molecular controls on Cu and Zn isotopic fractionation in Fe–Mn crusts [J]. Earth and Planetary Science Letters, 2014, 396: 213-222. doi: 10.1016/j.jpgl.2014.04.021
[42] Yang P, Post J E, Wang Q, et al. Metal adsorption controls stability of layered manganese oxides [J]. Environmental Science & Technology, 2019, 53(13): 7453-7462.
[43] Grangeon S, Manceau A, Guilhermet J, et al. Zn sorption modifies dynamically the layer and interlayer structure of vernadite [J]. Geochimica et Cosmochimica Acta, 2012, 85: 302-313. doi: 10.1016/j.gca.2012.02.019
[44] Hinkle M A G, Dye K G, Catalano J G. Impact of Mn(II)-manganese oxide reactions on Ni and Zn speciation [J]. Environmental Science & Technology, 2017, 51(6): 3187-3196.
[45] Hein J R, Koschinsky A, Kuhn T. Deep-ocean polymetallic nodules as a resource for critical materials [J]. Nature Reviews Earth & Environment, 2020, 1(3): 158-169.
[46] Wu F, Owens J D, Tang L M, et al. Vanadium isotopic fractionation during the formation of marine ferromanganese crusts and nodules [J]. Geochimica et Cosmochimica Acta, 2019, 265: 371-385. doi: 10.1016/j.gca.2019.09.007
[47] Bau M, Koschinsky A, Dulski P, et al. Comparison of the partitioning behaviours of yttrium, rare earth elements, and titanium between hydrogenetic marine ferromanganese crusts and seawater [J]. Geochimica et Cosmochimica Acta, 1996, 60(10): 1709-1725. doi: 10.1016/0016-7037(96)00063-4
[48] Bau M. Scavenging of dissolved yttrium and rare earths by precipitating iron oxyhydroxide: experimental evidence for Ce oxidation, Y-Ho fractionation, and lanthanide tetrad effect [J]. Geochimica et Cosmochimica Acta, 1999, 63(1): 67-77. doi: 10.1016/S0016-7037(99)00014-9
[49] Azami K, Hirano N, Machida S, et al. Rare earth elements and yttrium (REY) variability with water depth in hydrogenetic ferromanganese crusts [J]. Chemical Geology, 2018, 493: 224-233. doi: 10.1016/j.chemgeo.2018.05.045
[50] Bau M, Koschinsky A. Oxidative scavenging of cerium on hydrous Fe oxide: evidence from the distribution of rare earth elements and yttrium between Fe oxides and Mn oxides in hydrogenetic ferromanganese crusts [J]. Geochemical Journal, 2009, 43(1): 37-47. doi: 10.2343/geochemj.1.0005
[51] Marcus M A, Toner B M, Takahashi Y. Forms and distribution of Ce in a ferromanganese nodule [J]. Marine Chemistry, 2018, 202: 58-66. doi: 10.1016/j.marchem.2018.03.005
[52] Koschinsky A, Halbach P. Sequential leaching of marine ferromanganese precipitates: Genetic implications [J]. Geochimica et Cosmochimica Acta, 1995, 59(24): 5113-5132. doi: 10.1016/0016-7037(95)00358-4
[53] Josso P, Parkinson I, Horstwood M, et al. Improving confidence in ferromanganese crust age models: A composite geochemical approach [J]. Chemical Geology, 2019, 513: 108-119. doi: 10.1016/j.chemgeo.2019.03.003
[54] Puteanus D, Halbach P. Correlation of Co concentration and growth rate — A method for age determination of ferromanganese crusts [J]. Chemical Geology, 1988, 69(1-2): 73-85. doi: 10.1016/0009-2541(88)90159-3
[55] Manheim F T, Lane-Bostwick C M. Cobalt in ferromanganese crusts as a monitor of hydrothermal discharge on the Pacific sea floor [J]. Nature, 1988, 335(6185): 59-62. doi: 10.1038/335059a0
[56] Mcmurtry G M, Vonderhaar D L, Eisenhauer A, et al. Cenozoic accumulation history of a Pacific ferromanganese crust [J]. Earth and Planetary Science Letters, 1994, 125(1-4): 105-118. doi: 10.1016/0012-821X(94)90209-7
[57] Hein J R, Konstantinova N, Mikesell M, et al. Arctic deep water ferromanganese-oxide deposits reflect the unique characteristics of the Arctic Ocean [J]. Geochemistry, Geophysics, Geosystems, 2017, 18(11): 3771-3800. doi: 10.1002/2017GC007186
[58] Dutkiewicz A, Müller R D, Wang X, et al. Predicting sediment thickness on vanished ocean crust since 200 Ma [J]. Geochemistry, Geophysics, Geosystems, 2017, 18(12): 4586-4603. doi: 10.1002/2017GC007258