Or are you talking about a "Bitcoin address" in a wallet like MultiBit, Electrum, or Bitcoin Core?
NONo need to use caps. It's clear that you don't understand what you are asking about, and I'm just trying to get to the bottom of the problem so that I can explain it to you properly.
Are you talking about an "account" at a mining website, or at a service such as Coinbase?
No.
You appear to be confused about this. Here you are saying that it is not an "account" at a service such as Coinbase.
Yet right before that you say the opposite:
My coinbase account. I'm aware that bitcoin addresses aren't accounts.
Are you looking in your wallet? If so, what wallet are you using?
No, not looking at my wallet. It shows up when I input my bitcoin address into blockchain.info
Ok, now we're getting somewhere. Assuming that you are actually talking about an address that you use to fund a Coinbase account, and that you are actually looking at that address in blockchain.info, it is now clear exactly what is causing your confusion.
You've mistakenly assumed that the Coinbase service works like a bitcoin wallet, and that the address that you use to fund the Coinbase account is
your address.
Coinbase works more like a bank than a wallet. They provide you with one of their addresses which they link to an account that they've set up in their database for you. Whenever any bitcoins are sent to that address, Coinbase updates your "account" in their database to indicate that you have control over an increased amount of value. When you use their service to send bitcoins somewhere, what you are actually doing is making a request that they send on your behalf that many bitcoins that they control to the address you supply.
A bank doesn't keep all the deposited cash sitting in the drawer of the bank teller. For security purposes they regularly move cash out of the teller's drawer into a more secure vault. When the teller's drawer is a bit low on cash, they move some from the vault back into the teller's drawer. The cash that you withdraw from the bank isn't likely to be the exact same bills that you deposited. They are all mixed together in the vault and paid out as requested.
Coinbase similarly doesn't keep all the deposited bitcoins sitting in the address where it is received. For security purposes they regularly move bitcoins out of the deposit address into a more secure cold storage. When their hot wallet is a bit low on bitcoins, they move some of the cold storage back into the hot wallet. The bitcoins you "send" from the Coinbase service isn't likely to be the exact same bitcoins that you deposited. They are all mixed together in their cold storage addresses and paid out as requested. This is why you keep seeing the bitcoins moving out of the funding address. Coinbase is either moving those bitcoins into cold storage, or is using them as part of their hot wallet to make payments requested by others. When you make a request to send a payment, they'll use bitcoins that they receive from someone else.
As you can hopefully now see, you cannot use blockchain.info to track your balance at Coinbase. You have to trust Coinbase to properly maintain your balance in their database and to actually have all the bitcoins that they claim to have. If they are dishonest (or incompetent), there is potential for them to run fractional reserve (much like MtGox did). In this scenario, it is possible that the sum of all the balances in all the accounts is less than the total bitcoins that they actually have control over. If they are submitting to regular independent and trustworthy financial audits, it is very unlikely that they are running fractional reserve. It is up to you as a customer to demand proper auditing procedures and to check that those audits are occurring.